Christmas= crowds, but favorite time of year.
My family almost always goes around christmas time and I love it! My family has been so often, we usually go in the morning for extra magic hours, go back to the camp ground, then head over around 7pm and take advantage of the extra magic hours (usually til 2-3am) its desserted at that time. you can walk on alot of rides that usally have long waits. This past december I went to mk like 4 nites in a row after 7pm and go all the rides done. Its also better to arrive to the park after the fireworks, cause thats when most families leave.
It can get chilly, pants and jackets are a must. Even though its florida it does get down in the 30's. Make use of fastpasses, dining reservations (book as soon as you can), and dont be afraid to split up. I travel with a group of 8 and we split up for rides like Sm, tot, rnrc, tt, ev, etc.. Then join together for rides like HM, iasw, lvtl, KjS. It helps relieves stress and makes everyone's trip has good as possible.
Welcome to the boards and enjoy your trip!!! I'll be there myself. Be sure to check out the resorts decorations. if you have time, take a trip to the campground and go on the hay wagon ride (they don't use hay), which takes visitors around the campground to the trailers that have decorated for chirstmas. (my dad goes overboard, but so does alot of campers). Plus you can see the water parade. Enjoy!