Background: Very little is understood about the developmental antecedents of sexual behaviour prior to adolescence. Aims: Our aim was to examine the impact of different forms of intimate partner violence on early childhood sexual development. Methods: We used data from an ongoing prospective longitudinal cohort study of Canadian families. Intimate partner violence of various kinds was measured using a modified version of the Conflict Tactics Scale. Measures of child sexual development were based on the Child Sexual Behavior Inventory. Both measures relied on parental report. Results: Sexual coercion between parental figures, but not physical violence or emotional aggression, was significantly associated with intrusive sexual behaviours shown by 3- to 5-year-old children. Conclusions: It may seem unlikely that 3- to 5- year-old children can understand that their parents are in a sexually coercive relationship, but our findings suggest that they are sufficiently aware of such behaviours when they occur that they may start to model their own behaviour on them. Clinicians and social workers may need to be more aware of this possibility.