Sleep was examined as a process variable in relations between verbal and physical parent-child conflict and change in children's internalizing and externalizing symptoms over time. Participants were 282 children at T1 (M age = 9.44 years; 48% girls), 280 children at T2 (M age = 10.41 years), and 275 children at T3 (M age = 11.35 years). Children reported on parent-child conflict, sleep was assessed with actigraphy, and parents reported on children's internalizing and externalizing symptoms. Autoregressive effects for sleep and internalizing and externalizing symptoms were controlled to examine change over time. Supportive of intervening processes, physical parent-child conflict at T1 and increased change in internalizing and externalizing symptoms at T3 were indirectly related through their shared association with reduced sleep continuity (efficiency, long wake episodes) at T2. Findings build on a small but growing literature and highlight the importance of considering the role of sleep in relations between family conflict and child development.