Hi Meredith,
There is so much for children of all ages at each Walt Disney World theme park. I think that which Disney theme parks and attractions will be best for your children really depends on their unique interests. I suggest that you order the
free Walt Disney World planning DVD. By watching this, you can start to see what attractions you think will appeal to your children. Since you have four days of Disney theme park tickets, you could spend one day at each park, or your could decide to skip one or two and double up days at the theme parks that you think your children will enjoy most. Let me share with you some of the attractions that my daughter enjoyed the most at each Disney theme park when she was young.
At Magic Kingdom Park, you will probably want to spend lots of time in Fantasyland. My daughter loved "it's a small world" from the time she was an infant. Other favorites for all ages include The Many Adventures of Winnie the Pooh and Dumbo the Flying Elephant. At Epcot, young children may enjoy a ride through The Seas with Nemo & Friends followed by some time exploring the amazing pavilion filled with aquatic life, and then talking to Crush at Turtle Talk with Crush. Disney's Hollywood Studios is a great park for little ones who love Disney Junior Channel. You can have a meal with some of these characters at Play 'n' Dine at Hollywood & Vine, and then head to Disney Junior - Live on Stage!, a high-energy show filled with Disney Junior friends. At Disney's Animal Kingdom Park, my daughter always loved a ride on the Wildlife Express Train out to Rafiki's Planet Watch where she would interact with animals at Affection Section.
I would love to help you plan more, Meredith; however, I am limited in the space that I have to answer. Please do write back if you have any further questions!