This study investigated the ability of a psychosocial prevention program implemented through childbirth education programs to enhance the coparental and couple relationship, parental mental health, the parent-child relationship, and child outcomes. A sample of 169 heterosexual, adult couples expecting their first child was randomized to intervention and control conditions. The intervention families participated in Family Foundations, a series of eight classes delivered before and after birth, which was designed as a universal prevention program (i.e., applicable to all couples, not just those at high risk). Intent-to-treat analyses utilizing data collected from child age 6 months through 3 years indicated significant program effects on parental stress and self-efficacy, coparenting, harsh parenting, and children’s emotional adjustment among all families, and maternal depression among cohabiting couples. Among families of boys, program effects were found for child behavior problems and couple relationship quality. These results indicate that a universal prevention approach at the transition to parenthood focused on enhancing family relationships can have a significant and substantial positive impact on parent and child well-being.