This study examined how parents influence sex differences in young children's physical risk taking behaviors. Eighty three- and four-year old, mostly middle class and Caucasian children climbed across a five-foot high catwalk and walked across a three-foot high beam under their mother or father's supervision. Based on average preschooler gross motor capabilities, both of these activities posed potential threats to preschoolers' physical safety without proper parental monitoring. Analyses revealed that fathers of daughters monitored their children more closely than did fathers of sons. In contrast, mothers of daughters and mothers of sons monitored their children similarly. Differential treatment of preschool-aged girls and boys in risk taking situations is discussed as a contributor to sex differences found in children's physical risk taking and unintentional injuries.