my youngest is 4 and we have gone to Epcot since he was maybe 18 months. He loves the nemo ride, then the aquarium after.
My 3 kids have always loved walking around and seeing the countries and stuff. We found so many princesses in the countries with little or no wait. Snow white, Jasmine, Belle, Aurora, Mulan. my dd was thrilled she was maybe 5 or 6 when we first went to Epcot. but I am sure she will have plenty to see and take in
They also have the Character spot where you can meet Mickey, Minnie, Donals, Pluto, and Goofy. the most we have ever waited was maybe 30 minutes.