Hi Dena!
Oh, what a trip you guys will have! My daughter was 4 on our last trip and she had the time of her life! At 4 they are big enough to really get what's going on, to do most of the attractions and even old enough to push themselves a little---being tired, sugared and hot! It's SO fun! :)
I'm not sure what kind of tickets you have, but I suggest you do it all! Go to all 4 parks, hang out at your hotel and eat some fun meals!
The most important park is Magic Kingdom! It's got the castle and you just HAVE to be there! My daughter loved almost everything in Fantasyland (especially Dumbo and Mickey's Philharmagic). We did skip Snow White's Scary Adventure, though!
She also loved the Country Bears, meeting the Princesses and the Fairies and even Big Thunder Mountain!
Next, I suggest Animal Kingdom. It's got so many great shows (Finding Nemo, Festival of the Lion King, Tough to Be a Bug) and so many great interactive experiences (Safari, Jungle Trek, Exploration Trails, etc.). Plus, the ambiance is just great there!
Then I'd hit up Epcot or Hollywood Studios. Epcot has SO much to choose from--educational hands on experiences to you'll-think-you're-really-in-another-country adventures! Hollywood Studios has some great movie action attractions but also some Pixar stuff--Toy Story Midway Mania, Mater & Lightning, etc. And of course, Disney Junior LIVE!
I think you should try a character meal--either Chef Mickey's or Donald's Tusker House Breakfast. I'd also take one day off in between your park hopping to relax and hang out at the pool!
If you have any other questions, you can
ask me directly!