Hi there Kim!
Wow, you will really be doing it up that day! I'm sure the kids will be so excited! I would plan on getting to Cinderella's Royal Table as early as possible then try to go on the rides and shows that are not going to be operating during the party.
Around noon I would head back to the resort for a nice midday nap. I know the kids will be wanting to stay but, just remind them that they'll get to see Mickey and Santa during the parade at night!
Here is a list of the scheduled rides which should be open during the party... Oh and remember you can return for the party as early as 4:00 pm:
Tomorrowland:
Astro Orbiter
Buzz Lightyear's Space Ranger Spin
Monsters, Inc. Laugh Floor
Space Mountain
Stitch's Great Escape
Tomorrowland Speedway
Tomorrowland Transit Authority PeopleMover
Fantasyland:
Dumbo the Flying Elephant
It's A Small World
Mickey's PhilharMagic
Peter Pan's Flight
Prince Charming Regal Carrousel
Snow White's Scary Adventures
Liberty Square:
The Haunted Mansion
Frontierland:
Big Thunder Mountain Railroad
Country Bear Jamboree
Splash Mountain
Adventureland:
Pirates of the Caribbean
Swiss Family Treehouse
The Magic Carpets of Aladdin
And the scheduled shows and events during the party:
"A Totally Tomorrowland Christmas" Show: 7:45, 8:45, 9:55, 10:50 & 11:45 PM
Character Meet & Greets: 7:00 - 11:30 PM
"Celebrate The Season" Show: 7:45, 10:05 & 11:20 PM
Mickey's Once Upon A Christmastime Parade: 8:15 and 10:30 PM
Holiday Wishes Fireworks: 9:30 PM
I hope you have a Magical Time at the Walt Disney World Resort! Thanks so much for asking the Moms Panel! If you have more questions, we are always here to help!