Hi Stacy,
How exciting that you will be visiting Walt Disney World for the very first time and during the holidays which is most definitely the most magical time of the year!
As this will be your first visit, I would recommend that you spend one full day at each of the four theme parks and then re-visit your favourite park on your last day.
Here is my recommended itinerary:-
Saturday 10 December - Epcot
Sunday 11 December - Resort Pool/Mini Golf/Downtown Disney
Monday 12 December - Magic Kingdom
Tuesday 13 December - Disney's Hollywood Studios
Wednesday 14 December - Disney's Animal Kingdom
Thursday 15 December - Re-visit your favourite park
I would also consider purchasing tickets for
Mickey's Very Merry Christmas Party for Sunday 11 December. This is a super fun special event which is a lot of fun for the whole family.
I hope that this has been of help and wish you a magical trip!