The stages of change construct of the Transtheoretical Model have been successfully applied to examine physical activity adoption among adults. Thus far, little research on the stages of physical activity change has been focused on children. Therefore, the purpose of this study is to validate the stages of change with vigorous, moderate, and light physical activity, and sedentary behaviour among children. Two different samples (sample 1: n=513, 52% male; sample 2: n=258, 45% male) completed Godin's Leisure-Time Exercise Questionnaire and the physical activity stage questions. One-way ANOVAs revealed significant differences in both the samples between the stages of change for vigorous (sample 1: F=15.9, df=4508, p<.0125, eta(2)=.17; sample 2: F=12.8, df=4252, p<.0125, eta(2)=.11) and moderate (sample 1: F=8.54, df=4508, p<.0125, eta(2)=.07; sample 2: F=4.72, df=4252, p<.0125, eta(2)=.06) physical activity. There are no or weak correlations found between the stages of change and light physical activity (sample 1: F=3.12, df=4508, ns, eta(2)=.05; sample 2: F=3.38, df=4250, p<.0125, eta(2)=.02), or sedentary behaviour (sample 1: F=.54, df=4508, ns, eta(2)=.05; sample 2: F=3.13, df=4252, ns, eta(2)=.00). These results extend the validation of the stages of physical activity to children's moderate and vigorous intensity activities.