Background: Parental behavior can influence the development of overweight in children. The aim of this study is to examine whether parental BMI and parental physical activity are associated with BMI, waist circumference and physical activity in young children. Methods: In 3–4 year old children, weight, height and waist circumference were measured. Children’s physical activity was measured in a subgroup (n = 299) using a tri-axial activity monitor, Tracmor D . Data are represented as activity counts per minute (total physical activity) and as percentage of time in sedentary, light, moderate and vigorous intensity physical activity (generated from a subsample of Actigraph data using cut points from Butte et al.). Parental weight and height were self-reported and parental physical activity was assessed by the validated questionnaire SQUASH. Results: In total 1554 children (age 3.9 ± 0.1 years, BMI 15.8 ± 1.3 kg/m2 and waist circumference 52.4 ± 3.5 cm) were included. Eleven percent were overweight or obese. A higher maternal BMI was related to higher levels of children’s sedentary activity (r = 0.120, p = 0.04 and to lower levels of children’s total and moderate physical activity (r = −0.158, p = 0.007 and r = −0.154, p = 0.008, respectively). Parental BMI was positively correlated with children’s BMI and waist circumference (r = 0.20–0.27, p < 0.001). Higher maternal total physical activity levels were not related to children’s total physical activity level, but were related to higher levels of children’s moderate and vigorous physical activity (ρ = 0.132, p = 0.046 and ρ = 0.132, p = 0.046, respectively). No correlations between total, moderate or vigorous physical activity levels of the parents with the child’s BMI or waist circumference were found. Looking at physical activity domains maternal physical activity in active commuting, either walking or biking, showed a negative correlation with BMI of the child (ρ = −0.062, p = 0.042). Conclusions: Higher maternal BMI and lower maternal physical activity levels were related to lower levels of children’s physical activity. More active commuting by the mother and a lower parental BMI were related to a lower BMI of the children. Energy-balance related behavior of the parents may contribute to a healthier BMI of both preschool children and their parents.