There is little information about the onset and the developmental course of child sexual behavior problems (SBPs), including sexually intrusive behaviors (SIBs). Using data from the Vancouver Longitudinal Study on the Psychosocial Development of Children, the current study examined the presence of distinct patterns of sexual development among children. A normative sample of preschoolers ( N = 354) with a small clinical subsample were followed from age 3 to 8 with repetitive measurements of sexual behaviors using a revised version of Child Sexual Behavior Inventory. Semiparametric group-based modeling identified four distinct sexual development trajectories: the very low (10.5%), the low declining (27.8%), the moderate stable (48.3%), and the high-rate increasing (13.4%). In contrast to the other developmental trajectories found, the high-rate-increasing pattern showed that sexual behaviors became increasingly extensive after school entry. Children characterized by this developmental pattern, especially boys, were more likely to be involved in SIBs after elementary school entry than those in the other groups. Findings highlight the presence of multiple developmental trajectories of sexual development with significantly different behavioral patterns after school entry.