The purpose of this study was to investigate the relationship between dyadic and triadic family interactions and their association with the development of children's externalizing behaviors. Data were obtained from a longitudinal study of family interactions (N = 125), followed from before parents had their first child until children were 7 years old. Family interactions (marital, father–child, mother–child, and triadic mother–father–child) were observed in separate interaction tasks when children were 24 months old as predictors of children's externalizing behaviors at age 7 (n = 71 children). Results demonstrated that the triadic measure of competitive coparenting and the dyadic mother–child interaction characterized by negative emotional socialization related to children's later externalizing behavior, even after controlling for covariates and effects of all other family interaction variables. Results emphasize the importance of examining the family holistically and provided new information for designing more effective whole‐family interventions to reduce the development of children's externalizing behaviors.