We were there last Dec and it wasn't bad. We stayed at Port Orleans French Quarter and there were some families from Pop Warner at Riverside so we saw them on the bus. They were rather well behaved. I expected worse because of what people on here said. We did have a few cheerleaders yelling in the park, but it wasn't that bad. You will mostly see them on their off days when their team isn't playing and during EMH at night. Durning the day they are busy with the Super Bowl and cheering competitions. I think most of them stay at All Star Sports so if that's your resort you may concider switching or at least requesting a room away from them.
Have a great trip! Dec is a wonderful time to go! The parks and resorts are beautiful. It just felt a little strange to see all the Christmas stuff since I'd never been there that time of year before but after a day or 2 it was fine.