In recent years there has been growing concern about the increase in the numbers of overweight and obese children. In adults, obesity like other health problems appears to follow a social gradient with occupation, education and income being important predictors of obesity. However, in children the direct association between socio economic status (SES) and obesity is less clear while factors such as maternal weight and children's patterns of activity dominate. Drawing on sociological theory it can be argued that lifestyle may be an important mediator between SES and obesity because lifestyle is theoretically linked to social class and status. The aim of this study is to consider the associations between measures of parental socioeconomic status (occupation, income, education), and children's lifestyle and obesity in four-year old children. With children's lifestyle being predominantly measured in terms of the time children spend in a variety of sedentary (e.g. watching television) or active (e.g. walking or riding bicycles) activities. Analysis in MPLUS was conducted using questionnaire and diary data from Wave 1 of the Longitudinal Study of Australian Children (LSAC). A path analysis revealed complex associations between parental SES and children's weight status. Predominantly, there were two pathways. The first appears to work through maternal weight while the second works through the extent to which children engage in the sedentary activities of watching television or using a computer (screen time) (p<0.05). It is concluded that children's activities may mediate between parental SES and children's weight status.