This multistudy article examined the relative strength of mediational pathways involving hostile, disengaged, and uncooperative forms of interparental conflict, children’s emotional insecurity, and their externalizing problems across 2 longitudinal studies. Participants in Study 1 consisted of 243 preschool children (M age = 4.60 years) and their parents, whereas Study 2 consisted of 263 adolescents (M age = 12.62 years) and their parents. Both studies utilized multimethod, multi-informant assessment batteries within a longitudinal design with 3 measurement occasions. Across both studies, lagged, autoregressive tests of the mediational paths revealed that interparental hostility was a significantly stronger predictor of the prospective cascade of children’s insecurity and externalizing problems than interparental disengagement and low levels of interparental cooperation. Findings further indicated that interparental disengagement was a stronger predictor of the insecurity pathway than was low interparental cooperation for the sample of adolescents in Study 2. Results are discussed in relation to how they inform and advance developmental models of family risk.