Jindal I, Puyau M, Adolph A, et al. - Researchers intended to determine if there is an association between sleep duration, quality and timing in children, to the basal metabolic rate (BMR), total energy expenditure (TEE) and physical activity (PA). During school break (seven consecutive non-school days), 59 children in two age-groups (5-11 and 12-18 years) were evaluated for body composition (DXA), BMR in a room calorimeter, free-living TEE by doubly labelled water method, sleep and PA (7-day Actiheart monitor). After adjusting for age-group, gender, lean and fat mass, sleep duration contributed to the variance in BMR but not to the variance in TEE. Lower PA was associated with late sleep timing. Children in the younger age-group who met recommended sleep duration on ≥ 50% of the 7 days had higher light PA and lower sedentary time. Findings suggested an association of suboptimal sleep with lower BMR, lower PA, and higher sedentary behaviours in young children. Prospective research is needed to determine whether insufficient sleep duration or late sleep timing contribute to obesity risk by increasing sedentary behaviours and decreasing BMR.