I decided long ago not to mind his need for speed. Something about the movement itself feels good to him, so I let him go. I once asked him why he sprints everywhere and he simply said, "I just like to be quick."
At this age group, the goal is without a doubt more activity. But because it's also essentially a HIIT workout, which we know burns calories and fat while improving fitness levels, even adults could benefit from a little CrossFit for kids.