This study investigated the validity of the Caltrac accelerometer for estimating resting and exercise energy expenditure for children. Seventeen children 9 to 12 years of age participated in the study. Criterion values of energy expenditure were determined from measures of oxygen consumption (VO2) and respiratory exchange ratio (RER), and Caltrac estimates of energy expenditure were obtained concurrently for each experimental condition. Correlations were significant between Caltrac estimates and measured energy expenditure at rest (r = .53, p<.03) and at slow (r = .89, p<.001) and brisk (r = .85, p<.001) treadmill walking. The Caltrac overestimated caloric expenditure for rest (M = 7%; range = −8 to 36%) and also for both slow (M = 17%; range = −3 to 30%) and brisk (M = 25%; range = 5 to 46%) walking. However, because of the high validity coefficients during activity, and because of its practicality in field settings, the Caltrac may be useful in estimating daily resting and walking energy expenditure for groups of children.