This study has several limitations. Firstly, inadequate statistical adjustment (i.e., over- or under-adjustment) is always possible. Bias resulting from unmeasured or residual confounding may be present, especially given the complex set of social and biological factors that are correlated with maternal childbearing age. Loss to follow-up occurred in the later waves, particularly among women with a low household income, no job, smoking habits, and women of young maternal age. As these characteristics are often considered as risk factors for child health, the observed prevalence of outcomes within younger maternal age categories may have been underestimated. Recall bias from parental reporting of unintentional injuries and hospitalization admission during the past 12 months seems unlikely because the assessment is rather objective in nature.