The present study aims to address how dyadic and triadic family interactions across the transition to parenthood contribute to the later development of toddlers’ adaptive emotion regulation using structural equation modeling methods. Specifically, we examined the interrelations of observed marital negative affect before childbirth, parents’ emotional withdrawal during parent–infant interactions at 8 months, and coparenting conflict at 24 months as predictors of toddlers’ adaptive emotion regulation at 24 months. Data for the present study were drawn from a longitudinal dataset in which 125 families were observed across the transition to parenthood. Results suggested that prenatal marital negativity predicted mothers’ and fathers’ emotional withdrawal toward their infants at 8 months postbirth as well as coparenting conflict at 24 months postbirth. Coparenting conflict and father–infant emotional withdrawal were negatively associated with toddlers’ adaptive emotion regulation; however, mother–infant emotional withdrawal was not related. The implications of our study extend family systems research to demonstrate how multiple levels of detrimental family functioning over the first 2 years of parenthood influence toddlers’ emotion regulation and highlight the importance of fathers’ emotional involvement with their infants.