In low- and middle-income countries (LMICs), three-fourths of those aged three or four years lack -- nearly 182 million children -- access to adequate nurture, thereby risking healthy development, according to a new series paper, published in The Lancet journal.

The series builds on the foundation of the first 1,000 days of life -- referring to the time period starting conception until two years old -- and highlights how the 'next 1,000 days' (from age two to age five) is a crucial window of opportunity for providing nurturing care to children, researchers said.

During this stage of 'next 1,000 days', children are often not in direct regular contact with health or education services, with fewer than one in three children aged three or four attending early childhood care and education programmes in LMICs, said the researchers.

The authors called for an increased investment for this stage of child development, with a particular focus on improving access to high quality childhood care and education programmes, which should involve adequately paid and trained teachers and reasonable teacher-student ratios.

These programmes should also include child-centred play, evidence-based curricula, and warm, stimulating, and responsive classroom interactions, they said.

According to a new analysis, which is included in the Lancet series, providing one year of early childhood care and education for all children would cost on average under 0.15 per cent of the current gross domestic product of LMIC countries.

The series' authors said that the potential benefits of these programmes are 8-19 times higher than the cost of implementing them.

"This Lancet series has brought together global researchers who share a passion for early childhood development, and were keen to profile the 'next 1,000 days' as a crucial stage of development, especially in low- and middle-income countries (LMICs)," Catherine Draper, University of the Witwatersrand, South Africa, and co-chair of the Series said.

"Children from LMICs not only need to feature more strongly in research on the next 1,000 days, but should also be receiving the care they need to thrive. This includes supporting caregivers of young children, and ensuring that they have access to high quality early care and education programmes," Draper said.

Children not involved in childhood care and education programmes miss crucial nurturing care opportunities as roughly 80 per cent of interventions promoting healthy development are taking place in such settings, the authors said.

They added that the programmes offer a platform to combine yearly screening and growth monitoring, along with food assistance, nutrition supplements, and caregiver support.

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