As the deportees were led off the plane onto the steamy San Salvador tarmac, an anguished Araceli Ramos Bonilla burst into tears, her face contorted with pain: 'They want to steal my daughter!'

It had been 10 weeks since Ramos had last held her 2-year-old, Alexa. Ten weeks since she was arrested crossing the border into Texas and US immigration authorities seized her daughter and told her she would never see the girl again.

What followed — one foster family's initially successful attempt to win full custody of Alexa — reveals what could happen to some of the infants, children and teens taken from their families at the border under a Trump administration policy earlier this year. The 'zero-tolerance' crackdown ended in June, but hundreds of children remain in detention, shelters or foster care and US officials say over 200 are not eligible for reunification or release.

Federal officials insist they are reuniting families and will continue to do so. But an AP investigation drawing on hundreds of court documents, immigration records and interviews in the US and Central America identified holes in the system that allow state court judges to grant custody of migrant children to American families — without notifying their parents.

And today, with hundreds of those mothers and fathers deported thousands of miles away, the risk has grown exponentially.

States usually seal child custody cases, and the federal agencies overseeing the migrant children don't track how often state court judges allow these kids to be given up for adoption. But by providing a child's name and birthdate to the specific district, probate or circuit court involved, the AP found that it's sometimes possible to track these children.

Alexa peers over the back of her chair as her mother speaks during an interview in a park in San Miguel, El Salvador. (AP File)

Alexa's case began in November 2015 under the Obama administration, years before Trump's family-separation policy rolled out.

Her 15-month separation from her mother exposes the fragile legal standing of children under the care of the federal Office of Refugee Resettlement and a flawed, piecemeal system that can change the course of a child's life

It took 28 minutes for a judge in a rural courthouse near Lake Michigan to grant Alexa's foster parents, Sherri and Kory Barr, temporary guardianship. Alexa's mother and the little girl's immigration attorney were not even notified about the proceedings.

Based on their experiences with Alexa, the Barrs had become convinced that Alexa's mom was a bad mother and that the little girl would be abused if she were reunited with her.

'My wife and I are sick over this,' Kory Barr told the judge, who wished him good luck as he granted the foster parents' request two days after Christmas.

The federal system that had custody of Alexa said the state courts never should have allowed foster parents to get that far, no matter how good their intentions. But each state court system, from New York to California, runs wardship and adoption proceedings differently — and sometimes there are even variations between counties.

In Missouri, an American couple managed to permanently adopt a baby whose Guatemalan mother had been picked up in an immigration raid. That seven-year legal battle terminating the mother's parental rights ended in 2014.

In Nebraska, another Guatemalan mother prevailed and got her kids back, but it took five years and over $1 million in donated legal work.

The Office of Refugee Resettlement and Bethany Christian Services, the agency that placed Alexa in foster care, would not comment on her case. But Bethany said foster parents are informed they're not allowed to adopt migrant children.

Since the 1980s, however, Bethany acknowledged that nine of the 500 migrant children assigned to its foster program have been adopted by American families. The children, ages 3 to 18, were adopted after it was determined it wouldn't be safe or possible for them to go back to their families; at least one asked to be adopted by his foster parents, and another was a trafficking victim, Bethany said.

'We never want families to be separated,' Bethany CEO Chris Palusky said.

'That's what we're about, is bringing families together.'

John Sandweg, who headed US Immigration and Customs Enforcement under the Obama administration, said he worries that many more migrant children recently taken from their families may never see them again.

'We have the kids in the US and the parents down in Central America, and now they'll bring all these child welfare agencies into play,' Sandweg said.

'It's just a recipe for disaster.'

In Ramos' darkest days, she would lay on her bed, stare at the ceiling and sob, her hand on her stomach.

'This girl, she was here, in my womb,' she said. 'We are meant to be together. Always.'

Alexa's mother was born in the middle of a bloody civil war in El Salvador that gave way to violent street crime. She was pregnant at 13; that daughter was raised by grandparents.

Starting at age 19, Ramos had four sons with another man over the course of a decade, followed by the arrival of Alexa in 2013. She and her daughter looked alike — both bright-eyed, with dark hair framing their smooth skin.

It was after the children's father found another woman that the abuse began, Ramos said.

'The worst time was when he kicked me so hard it left a bruise and it never went away,' she later told an asylum officer. Without makeup, a dent in the centre of her forehead is apparent.

Ramos went to a shelter, but said she became increasingly convinced that her former partner would track her down and kill her. She applied for a US visa, she said, but got nowhere.

During a custody battle in their home city of San Miguel, Ramos said her children's father filed false police reports, including one alleging that she encouraged a 17-year-old girl to have sex with an adult. With the help of his own mother, who told authorities her son had made up the accusations, she successfully cleared her name and the cases were dropped.

Yet it was that information — later deemed 'outdated and unsubstantiated' by the US justice department — that was used in a Michigan court as support for the argument that Alexa should be permanently separated from her mother.

Ramos scraped together $6,000 to pay a smuggler who could help her escape from the man she said warned her she'd 'never be at peace.' On the month-long, 1,500-mile pilgrimage, she carried Alexa, a change of clothes, diapers, cookies, juice and water.

The toddler was exhausted by the journey. She slumped for days in a backpack carrier when they walked, and dozed and fidgeted when they travelled by car. When she was sleepy and agitated, she insisted on being cradled in her mother's arms.

After crossing the Rio Grande near Roma, Texas, Ramos and her 2-year-old were arrested by US Customs and Border Protection. Their ordeal appeared nearly over, since domestic violence was then considered grounds for asylum.

In El Salvador, Ramos might earn $5 a day selling clothes or waiting tables. In the US, she could earn more than that in an hour. Ramos yearned for a new beginning.

It took less than an hour for her hopes to shatter. The border agent screening her records spotted a red flag: She was a criminal, he said, charged in El Salvador. Alexa, crying, was pulled from her mother's arms.

'They told me I would never see her again,' Ramos recalled, her eyes filling at the memory.

She said she begged agents to send Alexa to friends in Texas, but said they gave up when two calls went unanswered.

Three days after their separation, court records show, the US government labelled Alexa an 'unaccompanied minor', which meant she entered the bureaucracy for migrant youth, typically teens, who arrive in the US alone. The toddler was issued a notice to appear on 'a date to be set, at a time to be set, to show why you should not be removed from the United States.'

At 28 months, Alexa was intelligent and engaging, but her vocabulary was limited to Spanish words for colours, some numbers and her favourite foods.

She initially was placed with a Spanish-speaking foster family in San Antonio, Texas, who would call Ramos in the detention centre and put Alexa on the phone.

'Each time they called, I could not stop crying,' Ramos said. 'Crying and crying, because I wanted to be with her.'

Over two weeks after their separation, ICE agents moved Ramos seven hours away to a rural Louisiana facility surrounded by high fences topped with coiled razor wire. While Alexa and her foster family decorated a Christmas tree, Ramos slept in a pod of bunkbeds.

Two months after her arrival there, Ramos used a translator to speak on the phone with an asylum officer who asked about her family, why she left El Salvador and what her children's father might do if she went back. Alexa was safe, Ramos told the officer, but 'I think he will kill me.'

The next day, Ramos got word that she had 'demonstrated a credible fear of persecution or torture,' according to the asylum supervisor at the Department of Homeland Security.

Her case was assigned to Oakdale Immigration Court in Louisiana, where the three judges had denied 95 percent of all asylum requests that year, compared to the national average of about 50 per cent. She said she called the list of pro bono lawyers she was provided, to no avail.

Without a lawyer, her chance at asylum slipped away. Like everyone else around her, she was being deported.

The federal government offers all deported parents the chance to take their children with them, but Ramos said she was ordered to sign a waiver to leave Alexa behind.

'The agent put his hand on mine, he held my hand, he forced me to sign,' she said.

Immigration agents then handcuffed Ramos and put her on a plane south, soaring over the volcanoes and jungles of Central America.

At the time, it was unusual for parents to be deported while their children remained behind in federal foster care, but that occurred again and again this summer.

More than 300 parents were deported to Central America without their children this summer, many of whom allege they were coerced into signing paperwork they didn't understand, affecting their rights to reunify with their children. Some parents also contended that US officials told them their children would be given up for adoption.

'And the reality is that for every parent who is not located, there will be a permanent orphaned child, and that is 100 per cent the responsibility of the administration,' US district judge Dana Sabraw said in August while overseeing a lawsuit to stop family separations.

The AP asked the state department, as well as embassy officials in El Salvador, Guatemala and Honduras, whether they were working with deported parents to find their children in the US.

The state department deferred to the Department of homeland security, which said in a statement: 'DHS is not aware of anyone contacting embassy or consulate in a foreign country to be reunified with a child. This is unsurprising given the fact that these parents made a knowing decision to leave their child in a foreign country.'

By April 2016, Alexa was transferred to the care of Bethany Christian Services, one of the nation's largest adoption agencies.

As thousands more Central American children crossed the border alone during President Barack Obama's second term, the non-profit agency's work providing temporary and long-term foster care to unaccompanied children had begun to grow.

Over the years, the Michigan-based agency has received support from local donors that include Education Secretary Betsy DeVos and her family members, who have contributed more than $3.1 million. One DeVos relative worked for Bethany, and another served on its board.

As the agency started receiving more Central American children, several former Bethany social workers said they were encouraged to recruit new foster families at the agency's traditional base, the Christian Reformed Church, and other local churches.

'All of a sudden when we had these younger kids to place, everyone was really excited about that,' said Sarah Zuidema, a former Bethany supervisor who grew up within the denomination. 'They just felt that if these kids could know Jesus, everything would be OK.'

Among the families who stepped up to help were the Barrs — Kory, a physical therapist at a nearby rehabilitation hospital, and his wife, Sherri, who ran a home-organization business. The Barrs had three daughters who were raised in a devout home and already had fostered two Salvadoran sisters in 2013.

Bethany's outreach to local families was part of a rising Christian movement to mobilise support to address what Bethany has called the 'global refugee crisis.'

The movement emphasises that fostering is aligned with spiritual beliefs, and urges families to approach the role with open hearts.

When Bethany placed Alexa in the Barrs' home, the couple signed a form promising they would not try to seek custody because the Office of Refugee Resettlement was legally responsible for the child. But eight months later, fearing for the girl's safety, that is exactly what they did.

On June 5, 2016, Alexa celebrated her third birthday 3,000 miles away from her mother. The next month, a social worker sent Ramos Facebook photos showing Alexa wearing an American flag tank dress, drawing outside in the Michigan sunlight. In another shot, the girl appears at the Barrs' front door clad in a hot pink ensemble, next to a little red wagon and the family dog.

Around this time, Alexa began meeting with a play therapist and, based on their observations of the girl, the Barrs became deeply suspicious that she had been exposed to abuse before she reached their home. Ramos said they then began limiting her phone contact with her daughter.

The foster programme notified the Michigan Department of Health and Human Services, which opened an investigation but decided the complaint lacked sufficient evidence.

Ramos had cried when social workers approached her about the abuse allegations and insisted that Alexa had always been safe in her care. Because Alexa had spent nearly a third of her life away from her mother, she then grew distressed at the thought that her daughter might have been harmed during their separation.

In August, the Young Centre for Immigrant Children's Rights, which has a federal contract to advocate for the best interests of immigrant children navigating the legal system, began investigating whether Alexa could safely be returned to her mother. An evaluator repeatedly visited Ramos and interviewed her family, neighbours and employer.

Meanwhile, Salvadoran diplomatic officials began making periodic visits to Grand Rapids to check on Alexa and advocate for her release.

'The foster family started putting up barrier after barrier to delay her departure,' said Patricia Maza-Pittsford, El Salvador's consul general in Chicago.

Finally, the girl's immigration attorney, the Department of homeland security and the US immigration courts all reached agreement: It was past time for Alexa to be back with her mother.

Just days before Christmas 2016, a federal immigration judge ordered her deported. The Barrs were told to pack up Alexa's things and have her ready to go at a moment's notice.

Alexa had learned to speak English, bonded with her foster sisters and captured their hearts. The Barrs were certain she had been abused and remain so to this day. So they hired a lawyer and went to court.

'The Office of Refugee Resettlement is planning to put Alexa on a plane back to her abuser,' the couple said in a handwritten application seeking guardianship. Alexa's mother, they wrote, 'has not owned her crimes, not been rehabilitated.'

During an emergency hearing, Kory Barr pounded on the judge's bench as he begged him to help them keep the girl in Michigan and insisted that child-welfare experts needed more time to investigate.

'Every day they are telling us this could happen very fast,' he said. 'We have her bags packed.'

Judge Mark Feyen confessed he wasn't familiar with the federal agencies involved, saying, 'This is kind of hard to pin down exactly who the interested parties are.'

Responding to their concerns that Alexa's life could be in danger, Feyen granted the Barrs temporary custody after their attorney, Joshua Mikrut, asserted he had a 'loose understanding' that a prior order had been issued suspending Ramos' parental rights, though he didn't know where. The judge asked him to return with proof, and also scheduled a full guardianship hearing for a few weeks later.

'Every time I get one of these, I learn a little more,' the judge said.

Within days, a federal immigration judge granted an emergency motion to stay Alexa's departure.

When state courts gain control of a child being detained by the federal government, that child can become invisible in the system. Alexa and her mother were held in federal custody. But states — not the federal government — typically run child-welfare systems.

Alexa's mom didn't know where to turn, and she didn't have the money to hire an attorney. But she did have Facebook.

Araceli Ramos walks with her five-year-old daughter in a park in San Miguel, El Salvador. (AP File)

In El Salvador, in the days surrounding the Michigan guardianship hearing, she posted a series of increasingly desperate videos — which went viral in Central America and in one case attracted 2.5 million views — speaking directly to the Barrs, to her daughter, to anyone who might help her get Alexa back.

'I'm the girl's mother. You aren't anything to her — you just met her because I travelled with her,' she sobbed in one video, her voice breaking as she addressed the Barrs. 'Look inside your hearts... I had her in my belly for nine months. I'm the mother and I'm waiting for her.'

In another video, she cried as she displayed dolls modelled on the Disney movie Frozen that she bought to give Alexa for Christmas.

Outraged and sympathetic comments poured in and word reached Salvadoran government officials in El Salvador and the Chicago consul's office. Pressure mounted.

A month after the Barrs were granted guardianship of Alexa, the justice department weighed in sharply.

'The Barrs obtained their temporary guardianship order in violation of federal law,' US prosecutors argued.

The Barrs' attorney and the Michigan judge also violated federal law by seeking and granting guardianship, and failed to inform Ramos or Alexa's lawyers about the proceedings, they wrote.

Over a month after they had petitioned to keep Alexa, Sherri and Kory Barr despairingly gave up. The federal government, they wrote the judge, 'seems to have us painted into a corner with no way out.'

While Mikrut acknowledges the Barrs sometimes were blinded by their passion, he said the federal system should allow challenges to its decisions about the welfare of children in its care.

A few days later, the Barrs sent Alexa home with a huge bag of toys and clothes and a letter from 'Papa Foster,' as Kory Barr called himself.

'Mi querida Alexa,' he began, or 'my dear Alexa.'

He wrote about how she loved her first snow, how they pretended to hold wrestling matches, how he cried at the thought of life without the 'baby' of their family.

'I hope this is not the last time we see you, but if it is, I want you to know that I will keep you in my heart forever,' he wrote.

Alexa was stunned when she landed in El Salvador in February 2017. Her mother sobbed and clung to her, but the girl barely recognised this woman who called herself Mama. When could she go home to 'Mama Foster, Papa Foster' and her three blonde, blue-eyed sisters? And what was this woman saying?

Alexa had lost all her Spanish and spoke English to her mother, using words like 'water' and 'chicken.' Ramos, who spoke almost no English herself, had to point to pictures or call friends to translate.

The Ramos' small brick home, shared with two of Alexa's brothers, is on a quiet dirt street a few blocks from the main drag, a colourful and chaotic mix of shops and services.

Alexa pined for her house in suburban Grand Rapids, its green lawn, her pink room. She rarely giggled and didn't want to play or eat.

Children traumatically separated from their parents are more likely to suffer from emotional problems throughout their lives, according to decades of scientific research. And some more recent studies have found that separation can damage a child's memory.

Ramos showed Alexa baby pictures to help her relearn their relationship.

'I am your mother. I love you so very much,' she told her in Spanish, over and over.

Slowly, over time, Alexa began to smile and understand her native tongue. She bonded again with her mother and brothers. Bright and energetic, she now often winds her small arms around her mother's waist and neck. When she wants attention, she whispers in her mother's ear.

Ramos still struggles with the pain of the separation, and to support her family on the few dollars a day she earns at a pizzeria. She often posts Facebook photos and videos of herself with her daughter, a visual assertion of their bond.

She fears for parents who were separated from their children under the zero-tolerance policy and has taken to Facebook to urge them to fight to get their kids back.

'If they give our children up for adoption without our permission, that isn't justice,' she said during a recent interview in a park. 'They are our children, not theirs.'

For months after she came home, Alexa asked if she could talk to the Barrs but Ramos wasn't ready. She had a change of heart when she learned Sherri Barr was ill and now lets them talk every so often.

'I do not feel resentment for them because they also love her and because the family is going through a bad time,' Ramos said. 'We all deserve an opportunity.'

The Barrs worry about Alexa's safety in El Salvador, but say they also worry about Ramos' well-being. They now consider their relationship with mother and daughter part of God's plan.

'No one wins in this one,' Sherri Barr said.