Hi Farron! Welcome to the Disney Parks Moms Panel.
I am glad to hEAR you are going to the Walt Disney World Resort with your little son. For a great start, I suggest you visit disneyworld.disney.go.com and download the Preschool Parent's Guide to Walt Disney World Resort. You can find there a lot of useful information for planning the most wonderful vacation.
Magic Kingdom Park is the best one for his age range. A breathtaking place, there are many attractions for him, parades and “meet and greet” opportunities with many Disney characters. I suggest you consider making an appointment at The Pirates League. He will have an unforgettable time being transformed into a real pirate!
Disney’s Hollywood Studios is my second choice for young kids. Park attractions are themed after Disney-Pixar movies and everyone’s favorite characters. Attractions and shows are so much fun. And the fireworks spectacle Fantasmic! is a "must-do".
Disney’s Animal Kingdom Theme Park is also a nice park for little kids. The place is beautiful, many animals and nature. There are some “must-do” attractions, such as Kilimanjaro Safaris, Finding Nemo – The Musical and Festival of the Lion King. My little daughter likes to spend at least one hour playing at The Boneyard, a special play area for small kids. You can also consider a character dining experience at Tusker House Restaurant, where you can meet Donald Duck and some of his friends for photos and autographs.
Epcot is a sensational Park, but can be very tiring for little ones. The area is big, you will have a lot of walking during your day. There are 11 pavilions representing different countries and IllumiNations: Reflections of Earth is an amazing fireworks show. I like to spend some time with my husband walking around the lagoon when I am there.
Hope this information helps your planning. Let us know if you have further questions.
Wishing you a wonderful day!
Gina V.