Well, I think even the strictest of discplinarians would balk at treating 5 year olds like an army platoon, and not just for reasons of "self-esteem." If you have any suggestions as how to organize a bunch of little kids who've just spent an hour playing baseball into a straight line and keeping their attention focused enough to find all the litter on the field, I'd love to hear them.
All I can say is that my team--and all the teams we play--pick up our messes after the games. We are dealing with little kids, here, though, so it's quite possible that some of the stuff gets stuffed under fences or hidden under bushes. Still, I'll remind my players again.