From the holistic environmental perspective, individual and environmental influences on low-income children's questionable development were identified and examined as to differences in the influences according to the child's developmental stage of infancy (age 0-35 months) or early childhood (age 36-71 months).

This study was a cross-sectional comparative design using negative binominal regression analysis to identify predictors of questionable development separately for each developmental stage. The sample was comprised of 952 children (357 in infancy and 495 in early childhood) from low-income families in South Korea. Predictors included individual factors: child's age and gender; proximal environmental influences: family factors (family health conditions, primary caregiver, child-caregiver relationship, depression in primary caregiver) and institution factors (daycare enrollment, days per week in daycare); and distal environmental influences: income/resources factors (family income, personal resources and social resources); and community factors (perceived child-rearing environment). The outcome variable was questionable development.

Significant contributors to questionable development in the infancy group were age, family health conditions, and personal resources; in the early childhood group, significant contributors were gender, family health conditions, grandparent as a primary caregiver, child-caregiver relationships, daycare enrollment, and personal resources.

Factors influencing children's questionable development may vary by developmental stage. It is important to consider differences in individual and environmental influences when developing targeted interventions to ensure that children attain their optimal developmental goals at each developmental stage. Understanding this may lead nursing professionals to design more effective preventive interventions for low-income children.