I've gone a couple of times when the Pop Warner kids are there. The main impact it seems to have on crowds is at some of the resorts, particularly the value and the moderate resorts. When I stayed at the POFQ a couple of years ago when they were there, there was a large number of football players and cheerleaders staying at the resort. They would sometimes run around the resort in small packs unsupervised and get a bit rowdy. Some mornings, they were practicing cheers or having loud tag football games in the courtyards around the resort. I only really noticed them a couple of times during my stay.
The other thing I've noticed is that sometimes there will be small groups of 6 or 8 kids running around the park unsupervised. As with many small groups of pre-teen, and early teenaged kids, some of them can get a bit obnoxious. I've had times when they've pushed and shoved in front of us, and one particularly obnoxious girl who kept on elbowing my cousin's six year old in the head when we were waiting in line for Test Track. The packs aren't usually too bad because you can usually get away from them on the next ride.
Karen