we went last year in December and it was awesome. To be honest, we didn't do a lot of swimming, though some days were certainly hot enough (not all days though, we had some cold days too) We never went to the waterparks (there just wasn't time)
Our daughter was 2 1/2 nearing 3 at the time and it is really different going with children. To be honest, I think it is a lot more fun, though every thing goes A LOT SLOWER!! If you keep that in mind it will be awesome, because seeing your kids respond to all the disney magic... that is just fantastic!!