With a child of my own interested in running a marathon, I researched marathon training programs for youth in the US (there are some!), injury rates and how these compare to high school running programs.
A little while ago I was working on a youth soccer certification. They talked a bit about the differences in warm-up/cool-downs related to different age groups. They didn't go too deep into but said roughly what you were describing. Pre-adolescent didn't really need much in the way of warm-up/cool-down and you could/should just "let 'em play". It wasn't until later that you didn't to be more on-task with that kind of thing to avoid injury.