Hi Jeanne!
It sounds to me like you guys will be having 3 times the fun at Walt Disney World!
For this age, our favorite
Character Dining experiences are Chef Mickey's, The Crystal Palace, and Cape May Cafe. Don't forget Cinderella's Royal Table for the Princesses - but truth be told, the Princes enjoy this one just as much!
Pick up the Times Guides at the entrance of each park each day for your favorite characters' appearance schedule. Another very magical way to see them is at the Character Parades, which I highly recommend you work into your daily itinerary when available.
We have some "family favorite" attractions in every Disney Resort Park that our children have enjoyed most at this age, and here are a few you may want to check out:
Magic Kingdom: Buzz Lightyear's Space Ranger Spin, Mickey's PhilharMagic, The Many Adventures of Winnie the Pooh, Pirates of the Caribbean, Dumbo, and it's a small world.
EPCOT: Journey Into Imagination with Figment, Turtle Talk with Crush, The Seas with Nemo and Friends, Character greetings all around the World Showcase, Gran Fiesta Tour at the Mexican Pavilion, and, if they meet the height requirement of 40 inches, Soarin'.
Hollywood Studios: Toy Story Mania!, Disney Junior Live on Stage, Voyage of the Little Mermaid, Muppet Vision 3-D, Honey I Shrunk the Kids Movie Set Adventure
Animal Kingdom: It's Tough to be a Bug, Camp Mickey Minnie, Kilimanjaro Safaris, Festival of the Lion King, Finding Nemo - The Musical, The Boneyard, TriceraTop Spin, Wildlife Express Train, and, if they meet the 38 inch height requirement & don't mind getting wed, Kali River Rapids.
I hope this information is helpful in getting your started!