We arrived in WDW on Thanksgiving Day last year. Didn't go to a park until the day after. It was really the most crowded I have ever seen it. But, since I have only been in late Oct/early Nov and mid August, I wasn't surprised it would be more crowded.
By Sunday the crowds did start to diminish. We left on Wed, Dec 1. I would have killed to have been able to stay through the week. By the time we left the parks were really wonderful!!! No big crowds at all. I think you will find that week to be really nice. The weather was wonderful, the holiday decorations were beautiful.
As far as any cheerleaders/football players/dancers go...we were there with them in Dec '03. We stayed at AllStarMu with them also. I never had an issue with the kids. They weren't evident in the parks very much, especially during the day, until their last week-end. I wouldn't worry too much about the kids being there or not. I certainly wouldn't change my plans based on them.