Guided by emotional security theory, this study examined the family-level antecedents of children's reaction patterns to interparental conflict in a sample of 243 preschool children (M age = 4.60 years; 48% Black; 16% Latinx; 56% girls) and their parents in the Northeastern United States. Behavioral observations of children's responses to interparental conflict over two annual measurement occasions assessed their tendencies to exhibit four patterns of defending against threat: secure (i.e., efficiently address direct threats), mobilizing (i.e., high reactivity to potential threat and social opportunities), dominant (i.e., directly defeat threat), and demobilizing (i.e., reduce salience as a target of hostility). Latent profile analyses of interparental, coparental, and parent characteristics derived from multiple methods at the first wave yielded four profiles corresponding with harmonious, enmeshed, compensatory, and detouring patterns of family-level functioning. Additional analyses revealed that children in harmonious and compensatory family profiles exhibited more secure patterns of reactivity over a 1-year period than children in the enmeshed family profile. In contrast, subsequent mobilizing reactivity was most pronounced for children in the enmeshed family profile. Finally, children in the detouring profile exhibited substantially higher levels of demobilizing reactivity to interparental conflict. Results are discussed in the context of how they inform and refine emotional security theory.