The purpose of the study is to evaluate the validity of different SenseWear software (algorithms v5.2 vs. algorithm v2.2) for estimating energy expenditure (EE) in children.Original research.Forty-five children aged 7–13 years performed 12 randomly assigned activities (out of a set of 24) while wearing a SWA with simultaneous monitoring via portable calorimetry (IC). Each activity lasted 5min, with a 1min break between activities. The estimated EE values from the SWA were compared to the measured EE values from the IC using 3-way (Method×Algorithm×Activity) mixed model ANOVA.The analyses revealed a significant method (IC vs. SWA)×Algorithm (v5.2 vs. v2.2) interaction, with significantly smaller errors (IC-SWA) for the newer v5.2 algorithms (0.25±0.09kcalmin−1) than the older v2.2 algorithms (1.04±0.09kcalmin−1). The mean absolute percent error (MAPE) was 17.0±12.1% for SWA5.2 algorithm and 31.4±11.1% for SWA2.2 algorithm. The v5.2 algorithms yielded non-significant (p>0.5) differences in EE estimates for most of the walking related activities as well as for stationary cycling at moderate intensity (MAPE=14.5%).The smaller errors in estimated EE with the SenseWear v5.2 algorithms (compared to v2.2) demonstrate continued incremental improvements in estimates of EE for monitoring free-living activities in children.