We love December because the crowds are very light. As far as weather goes, it is so unpredictable, you will have to check the weather before you leave. One year it was absolutely fabulous -- 70-80 during the day and 70 at night. It was the best. We never needed our long pants or jackets. The next time we went, it was cold. Never wore our shorts. Kids did swim in the pool but the weather was in the 50s. The pool is heated. And on the last day we even wanted hats, mittens and a thicker jacket. Then we went when the weather was continuous rain. In the winter, Florida has more than just a quick shower and it's over. It rained all day, every day. Not the best time. But I still continue to think December is the best time of the year to go. Low crowds, very festive, and definitely not too hot. Again, check the weather before you leave and bring a little of everything.