Changing Longitudinal Associations Between Home-Rearing Environments and Child Developmental Atypicality Across Two Decades

Home-rearing environments are integral to early childhood development. However, it remains unclear whether their developmental significance has changed over time. This study aimed to examine the temporal changes in home-rearing environments and their longitudinal associations with child developmental atypicality in Japan, using baseline assessments from 1999 to 2023 and follow-up assessments through 2024. Data were obtained from the Japanese Childcare Cohort Study, a nationwide childcare-based developmental surveillance project. The analysis included 40,627 1-year observation pairs of 18,210 children enrolled in childcare centers. Home-rearing environments were assessed using the Index of Child Care Environment, and developmental atypicality was evaluated using the Child Development Scale across six domains. Logistic regression models were used to examine the associations between baseline home-rearing environments and developmental atypicality 1 year later, adjusting for baseline developmental status, sex, and age. Generalized additive models and rolling-window analyses were used to assess temporal trends and time-varying associations. Overall, the Index of Child Care Environment scores increased gradually throughout the study period, although social stimulation declined after the mid-2010s. Higher-quality home-rearing environments were generally associated with a lower risk of subsequent developmental atypicality. Protective associations strengthened over time, particularly in the social, communication, vocabulary, and intellectual domains. Home-rearing environments and their developmental implications changed over the 25-year observation period. These findings highlight the continued importance of promoting direct caregiver–child interactions, including shared activities and social engagement. Early childhood surveillance should be periodically re-evaluated to remain relevant to evolving caregiving practices and family contexts.