There are no previous reports of energy expenditure and perceived effort during brisk-walking and running at speeds self-selected by young children. Fifty four participants (age 8-11 years old) performed 1500 m of brisk-walking and running in a marked school playground, and were given simple instructions to either 'walk quickly' or to 'jog'. During the running the children achieved higher mean speeds and a greater total energy expenditure (p < .001). However, there was no difference in the perceived effort between the two activities (p > .05). These findings suggest that under certain conditions children find it just as easy to run as they do to walk briskly, even though the speed and energy expenditure is significantly higher.