Background: The purpose of this pilot study was to assess the feasibility of a structured activity protocol in a room calorimeter among young children. Methods: Five healthy children (age 5.2 ± 0.4 y) performed an activity protocol in a room calorimeter, ranging from sedentary—to vigorous-intensity activities. Energy expenditure (EE) was calculated from continuous measurements of O2-consumption and CO2-production using Weir’s formula. Resting EE was defined as EE during the first 30 min of the study where participants were seated while watching television. The children wore an ActiGraph accelerometer on the right and left hip. Results: The protocol was well tolerated by all children, and lasted 150 to 175 min. Further, differences were seen in both EE and accelerometer counts across 3 of the 4 activity intensities. Conclusions: It is feasible for young children to perform a structured activity protocol in a room calorimeter enhancing the possibility of conducting future studies to cross-validate existing accelerometer prediction equations.