Background This study aimed to examine prospective associations of young infants' home environments with expressive vocabulary delay and internalising and externalising problem scores independently of family socioeconomic status (SES) and national origin.

Methods Prospective data from fetal life to age 3 were collected in a total of 2711 families participating in the Generation R Study, a longitudinal population-based cohort. Infants' home environments (ie, the learning environment and the physical environment) were assessed exclusively by observation in their first few months of life (mean age=3.38 months, SD=1.17). Internalising and externalising problems were measured at age 1.5 and 3; expressive vocabulary delay was assessed at age 2.5. Family socio-demographic characteristics, including SES variables and national origin, were measured during pregnancy.

Results Lower quality learning environments of young infants, but not physical environments, were associated with expressive vocabulary delay and more internalising problems in toddlerhood independently of SES and national origin. Associations of SES and national origin with children's outcomes were reduced when the home environmental variables were added to the regression model.

Conclusions The current findings suggest that SES and national origin are reflected, to some degree, in the quality of infants' home environments. Some of the possible interpretations of these results are discussed together with their implications for the early identification of children at risk of impaired development.