--- - |2+ Omega‐3 supplementation has been found to reduce externalizing behavior in children. Reciprocal models of parent‐child behavior suggest that improving child behavior could lead to improvements in parent behavior, however no study has examined whether omega‐3 supplementation in children could reduce intimate partner violence or child maltreatment by their adult caregivers. In this randomized, double‐blind, placebo‐controlled, stratified, parallel group trial, a community sample of children were randomized to receive either a fruit drink containing 1 gm of omega‐3 fats (Smartfish Recharge; Omega‐3 group, n = 100) or the same fruit drink without omega‐3's (Placebo group, n = 100). Child participants, adult caregivers, and research staff were blinded to group assignment. Adult caregivers reported inter‐partner and child‐directed physical assault and psychological aggression at baseline, 6 months (end of treatment) and 12 months (6 months post‐treatment) using the Conflicts Tactics Scale. Caregivers of children in the omega‐3 group reported long‐term reductions in psychological aggression in a group × time interaction. Improvements in adult psychological aggression were correlated with improvements in child externalizing behavior scores. No differences were reported for child maltreatment. This study is the first to show that omega‐3 supplementation in children can reduce inter‐partner psychological aggression among adult caregivers not receiving supplements. Findings suggest that improving child behavior through omega‐3 supplementation could have long‐term benefits to the family system as a whole. - Aggressive Behavior, Volume 44, Issue 5, Page 491-500, September/October 2018.