Research has demonstrated the importance of early family characteristics, such as the quality of caregiving, on children’s later mental health. Information is, however, needed about the role of more holistic family systems and specific child-related socioemotional mechanisms. In this study, we conceptualize families as dynamic family system types, consisting of both marital and parenting trajectories over the transition to parenthood. First, we examine how early family system types predict children’s anxiety, depression, peer exclusion, and emotion regulation. Second, we test whether couples’ infertility history and other family related contextual factors moderate the effects of family system types on child outcomes. Third, we test whether children’s emotion regulation and peer exclusion mediate the effects of family system types on anxiety and depression. The participants were 452 families representing cohesive, distant, authoritative, enmeshed, and discrepant family types, identified on the basis of relationship autonomy and intimacy from pregnancy to the child’s age of 2 and 12 months. Children’s anxiety, depression, emotion regulation, and peer exclusion were assessed at the age of 7–8 years. Structural equation modeling showed that distant, enmeshed, and discrepant families similarly predicted children’s heightened anxiety and depression. Infertility history, parental education, and parity moderated the associations between certain family system types and child outcomes. Finally, emotion regulation, but not peer exclusion, was a common mediating mechanism between distant and enmeshed families and children’s depression. The results emphasize the importance of early family environments on children’s emotion regulation development and internalizing psychopathology.