Hi Rebecca!
Thank you for bringing your question to the Disney Parks Moms Panel!
What a sweet age for your son to visit Walt Disney World Resort! He will be old enough to get super excited when he sees some of his favorite characters in real life.
I highly suggest that you make
Magic Kingdom Park your first stop. This is the quintessential "Disney" park and has fun attractions geared toward preschool-age children. You can easily spend an entire day here and still have more to explore! This link takes you to
lists of attractions at the Walt Disney World theme parks. You can sort them by age, interest, etc.
The second park I would recommend is
Disney's Hollywood Studios. There, you can
meet your favorite Disney Junior pals, as well as see the
Disney Junior Live On Stage show. Soon, at Hollywood Studios, you'll be able to explore Andy's Backyard in the brand new
Toy Story Land! I am so excited for this land to open!
All four of the parks will have something for him to enjoy, but these would be my suggestions.
I hope this helps!
~Lori