Sleep problems in early childhood are relatively common and are associated with later behavioral, affective, and cognitive problems. The current study examined two family process predictors of change in child sleep problems from 9 months to 4.5 years in an adoption sample: marital hostility and hostile parenting. Participants were 361 linked triads of birth mothers, adoptive parents, and adopted children. We examined direct and indirect pathways from marital hostility to child sleep via hostile parenting, whether child sleep problems were directly influenced by birth mother internalizing disorders (indicating genetic influences), and whether associations between marital hostility, hostile parenting, and child sleep problems were moderated by birth mother internalizing disorders. Hostile parenting at 27 months was associated with child sleep problems at 4.5 years, and a significant indirect effect was found from marital hostility to child sleep problems at 4.5 years via hostile parenting at 27 months. There was no direct effect from marital hostility at 9 months to child sleep problems at 4.5 years or for birth mother internalizing disorders on child sleep problems. The findings suggest targets for prevention/intervention programs that are potentially modifiable (e.g., hostile parenting, marital hostility), and inform theory by demonstrating that relations among marital hostility, hostile parenting, and child sleep problems are significant after accounting for the effects of shared genes among family members.