I recently got really into rock climbing and there are some young kids who are extremely good at the gym I climb at. I actually end up climbing with some of them as we share tips on how to solve problems. I think it's probably a lot more healthy for the mind and body than some of the youth sports competition. There are "leagues" and "teams" but it's much more you vs the wall or you vs the mountain. It's also much better exercise than every sport I've ever played except wrestling which is very similar in terms of the total body muscles used and stamina required. Every one of these kids age 8-18 I see climbing is in incredible shape like an elite wrestler would be and they got that way just by climbing around having fun challenging themselves.
Friends of ours own and operate a Ninja Warrior gym here in MSP. The wife has been on the show multiple times. They have a kids league as well. Seems like its just as good as other youth sports. It's similar to running track in that it's about individual performance but it gets rolled up into a team competition. Those kids are all very functionally strong and fit.