Hi Jennifer!
The great thing about Walt Disney World Resort is that all of the theme parks are perfect for children of any age! For a quick day trip, I would recommend
Disney's Hollywood Studios, because your son will be able to enjoy the
Disney Junior - Live on Stage! show with his favorite Disney Junior characters (Mickey Mouse Clubhouse, Handy Manny, Little Einsteins and Jake and the Neverland Pirates). He can then enjoy dining with those same characters at
Disney Junior Play 'n Dine at Hollywood and Vine for breakfast and lunch. I think that he could also enjoy rides such as
Toy Story Mania.
If you are able to enjoy an additional day in the parks, I would recommend
Magic Kingdom Park. He will love all that the park has to offer from the characters to the rides that are appropriate for his age.
Please let us know if you have additional question, we would love to help! Have a magical day!
Raquel