This pilot study pursued three objectives: to assess the effect of a 1-month multilevel intervention on the PA of children, to assess the impact of the intervention on the theory of planned behavior (TPB) variables, and to evaluate the extent to which the impact of the intervention on PA and TPB variables varied according to personal (i.e., gender and age) and situational (i.e., class and school) moderating variables. Children were aged 7 to 11 years (n = 306). Analyses revealed a significant increase of PA practice and TPB variables (ps < .001). Age (i.e., being a younger child) was associated with a higher increase on attitude and perceived control (ps < .01). The class or the school levels explained a meaningful variance in the evolution of PA or TPB variables (intraclass correlation coefficients > .10). The present study reports the interest and feasibility of a multilevel intervention to increase PA and TPB variables in children.