Nationwide insights on early childhood neurodevelopment during a global health crisis: evidence from COVID-19 in South Korea

Background: The COVID-19 pandemic has disrupted early childhood environments globally, raising concerns about its potential impacts on neurodevelopment. Although early childhood is a critical developmental period, large-scale evidence from South Korea - where strict social distancing and unique caregiving structures were in place - remains limited. We aim to evaluate age- and domain-specific neurodevelopmental outcomes among children aged 0-5 years before and during the pandemic, focusing on differences by age and sex. Methods: We analysed children aged 0-5 years using data from a national health screening programme and a pre-post comparison design with repeated cross-sectional data. We compared the pre-pandemic (July 2018-March 2020) and pandemic (April 2020-December 2021) periods. We categorised children into infants (9-12 months), toddlers (18-36 months), and preschoolers (42-71 months). We measured developmental outcomes using the Korean Developmental Screening Test across six domains: gross motor, fine motor, cognition, language, social skills, and self-help. We conducted multivariable logistic regression and difference-in-differences analyses. Results: We analysed 6 253 076 assessments from 2 797 459 children. Peer-level developmental status declined significantly during the pandemic across all age groups, with the most pronounced decrease among toddlers (adjusted odds ratio (aOR) = 0.92; 95% confidence interval (CI) = 0.91-0.92), followed by infants and preschoolers. The language domain experienced the greatest decline (aOR = 0.87; 95% CI = 0.86-0.88), whereas the gross motor domain showed significant improvement (aOR = 1.13; 95% CI = 1.11-1.15). Boys were more adversely affected than girls, particularly in gross motor and social skill domains. Conclusions: The COVID-19 pandemic led to significant developmental declines among young children, particularly in language and social domains and among toddlers. Boys were more adversely affected than girls, especially in language and socioemotional skills, highlighting sex-related vulnerabilities. Prioritising early screening and interventions targeting these key domains, alongside sex-sensitive strategies and caregiver support, will be essential to mitigate developmental disruptions during future pandemics.