Background: Implications of early attachment have been extensively studied, but little is known about its long-term indirect sequelae, where early security organization moderates future parent-child relationships, serving as a catalyst for adaptive and maladaptive processes. Two longitudinal multi-trait multi-method studies examined whether early security amplified beneficial effects of children's willing, receptive stance toward the parent on socialization outcomes. Methods: We examined parent-child early attachment organization, assessed in the Strange Situation at 14-15 months, as moderating links between children's willing stance toward parents and socialization outcomes in Study 1 (108 mothers and children, followed to 73 months) and Study 2 (101 mothers, fathers, and children, followed to 80 months). Children's willing stance was observed as committed compliance at 14 and 22 months in Study 1, and as responsiveness to the parent in naturalistic interactions and teaching contexts at 25 and 67 months in Study 2. Socialization outcomes included children's internalization of maternal prohibition, observed at 33, 45, and 56 months, and maternal ratings of children's externalizing problems at 73 months in Study 1, and mothers' and fathers' ratings of children's oppositional defiant disorder and conduct disorder symptoms at 80 months in Study 2. Results: Indirect effects of attachment were replicated across both studies and diverse measures: Attachment security significantly amplified the links between children's willing stance to mothers and all outcomes. Secure children's willing, cooperative stance to mothers predicted future successful socialization outcomes. Insecure children's willing stance conferred no beneficial effects. Conclusions: Implications of early attachment extend to long-term, indirect developmental sequelae. Security in the first year serves as a catalyst for future positive socialization processes.