Amanda,
The real question is what Disney characters do they want to see the most?
If they are into all the princesses, then the best choice is
Restaurant Akershus. Numerous princesses visit here to make that the start to your day at Epcot a magical one.
If they just want to see Cinderella, then
Cinderella's Royal Table in the Magic Kingdom is the place to go.
For Winnie the Pooh, the
Crystal Palace is a great buffet experience, right in the heart of the Magic Kingdom.
For Playhouse Disney characters like the Little Einstein's, there is
Hollywood and Vine at Hollywood Studios.
Lilo and Stich have breakfast at
'Ohana in the Polynesian.
1900 Park Fair in the Grand Floridian has Mary Poppins and Alice in Wonderland in the morning, and Cinderella at dinner.
And of course for Mickey and his pals, you have
Chef Mickey's at the Contemporary Resort,
Cape May Cafe at the Beach Club, and
Donald's Safari Breakfast at the Animal Kingdom.
My favorites are Chef Mickey's, Donald's Safari Breakfast, and Restaurant Akershus, but they are all special in their own way.
I am glad to answer any follow-up questions!
Have a magical (and delicious) vacation!