176 boys and 169 girls aged 8-9 years old took part in a longitudinal study of associations between eating behaviours, PA and weight gain during childhood. Height, weight and waist circumference were measured, and PA data were collected using an Actigraph worn for 5 consecutive days. In boys, physical activity was progressively lower across the weight spectrum, but in girls physical activity was consistently low across all weight categories. Intervention is required prior to 8 years old to prevent weight-related declines in physical activity in boys and further research is required to determine at what age, if ever, weight related differences in physical activity are apparent in girls.