I grew up going to Disney at Christmas time. We have no family in here, and it was too much to fly 'home' to Wales, so we went to Disney...lol Like pp said it is BUSY!! You cannot really understand it until you see/witness it. But the magic that surrounds it is amazing. You get all the Disney magic rolled up with the excitment of Christmas. I haven't been to Disney at Christmas for about 12 years though. I have been in the first few weeks of December, and that is great, low crowds and mild weather. I know that isn't an options for you with your kids needing to vacation during their school breaks..
Just get a plan, and be flexable. We made use of the parade/fireworks showtimes to do rides. Remember to be patient, even though you are at the 'Happiest Place on Earth', not many people act like it!!