Hello, Shalane,
Visiting between Thanksgiving and Christmas is my ideal time to visit as long as you can actually stay away from those specific holidays when schools aren't in session. The time between the holidays is typically less crowded with lower room rates, but filled with incredible holiday decorations throughout all the parks and resorts I truly adore visiting the Walt Disney World resort at this time.
The temperatures can vary during this time. The average temperature in December is 62 degrees, but it can still vary. For example when we were there last December, we had a couple days in shorts and a couple of other days where we wore jackets and pants during the day. Because of this, I'd encourage you to follow the weather forecast prior to your arrival on a site such as www.weather.com.
Just an fyi, you may have an opportunity to dine at one of the newest restaurants in Fantasyland:
Be Our Guest, which is scheduled to begin taking reservations in late August.
If you have more questions as you continue to plan your trip, please let us know. We are happy to help.