Hi Laura,
There really are so many choices for you. I would opt to split your time between Magic Kingdom and Epcot. Both of these have great attractions for everyone in your party as well as parades and magical photo opportunities.
Magic Kingdom is the place Walt Disney wanted all families to enjoy together. Fantasyland is a fun place for families to relax and have fun. Epcot has some of the best dining in Walt Disney World and you will feel like you are touring the world in World Showcase. Plus the holidays are the best in World Showcase as you experience all the winter holidays around the world.
If you like animals, than Animal Kingdom is a great place to tour with little ones as it has outdoor attractions and great shows.
While Disney's Hollywood Studios does have a show geared for toddlers, I might save this park for when they are older.
Finally, Downtown Disney is great for shopping for your holiday gifts and do not forget the resorts for their own special magic!
Wishing you a magical vacation!
Beth