Hi Codi,
You are going to Walt Disney World at a beautiful time of year. The theme parks will be decked out for the winter holidays, and are absolutely lovely. As I am sure you can imagine, this is also a very busy time of year at Walt Disney World. A bit of careful planning should help you to make the most of your vacation.
When I am looking for crowd predictions and specific parks to visit on specific days, I visit the unofficial website touringplans.com. For a small fee, you can gain access to their theme park crowd predictions and suggestions. Possibly the best days to visit Magic Kingdom would be December 23 and 25. This would leave you with December 24 for Disney's Hollywood Studios, and December 22 or 26 for Disney's Animal Kingdom. Please know that all of the theme parks will be crowded at this time, no matter which you choose to visit on each day.
You mention that you would like to dine at Magic Kingdom on December 24 or 25. I do suggest that whichever day you choose, that you make a reservation as soon as possible. Since the theme parks will be very full, the dining options will likely fill up sooner. You can make a dining reservation by visiting
Disney Dining Reservations online or by calling 407-WDW-DINE (407-939-3463).
A couple more quick tips for you: first, be sure to go to the theme parks early. Although they will be crowded, crowds are typically at their lowest in the hour or two after opening. Also, since you will be celebrating your birthday, be sure to get a free birthday button from Guest Relations at one of the theme parks. It is so much fun to have cast members and other guests wish you a happy birthday throughout the day!
I hope that these suggestions are helpful for you, Codi. Have a great time planning your visit to Walt Disney World, and please do not hesitate to ask if you have any further questions.