I have stayed in the first week of December, back in 2014 and I noticed nothing from 'Pop Warner'. I actually thought that week was less crowded than week 2 in December, by far, and that is what most of the crowd calendar websites say as well - it only gets more crowded as the month goes on, not less. But anyway, unless you're staying in one of the value resorts, and maybe a couple of mods (you can look up where the Cheer competitors and Pop Warner people are staying quite easily before you plan their trip since they announce it on their website) it is highly unlikely you will see or notice any of them. And they don't stay at all the values either - like I don't think they stayed at Art of Animation or Pop Century this year.
I would research what they say on the various Disney calendar sites like **************.net and others. You can do a google search for best weeks to go to Disney World and compare and contrast.
I'm trying the last week of January and the first week of February this year and relatively speaking, those are supposed to be two of the "least crowded" weeks there are as there's nothing of note going on at all. Generally, try to avoid Disney when the kids are off from school or during any holidays or school breaks or during special events if the MOST important thing for you is low crowds. But it's Disney - no matter what you must expect crowds. You can do only so much to minimize this. Disney will never be empty. If there's a time of year that is the right price or right time for you, personally, take that into consideration as well. Weigh it all - not just the crowds because it's always some level of busy.
Like, I had the opportunity to tag along with my sister and her family on winter break several years ago in February, breaking one of the "cardinal rules" of when to go, a holiday and a week when the kids were off (this was back in '09) and I have to tell you, it was fine, crowds-wise. Or maybe it takes alot to rattle me. But sometimes sites like these (which I love) tend to...rather complain alot and scare you on issues like crowds...to the point of you expecting to be stampeded or something when you go. It wasn't that bad, really, and I got to save on room fees because my sister had a time-share. And I didn't notice much of anything extreme in terms of waits other than what was expected for the popular rides at peak times of the day.
Really, you can enjoy most of Disney most of the time...the most important thing that is always said is not what day of the calendar you go so much as what time of day you visit the parks - get there at rope drop and hit the popular stuff you wanna go on early and then enjoy a lunch/siesta by early afternoon when the crowds are at their peak and save those fast passes for when you return.
