Hi Bridgette!
My family is living proof that children even younger than three can enjoy the rides at Disney World! My daughter's first trip to Disney was when she was 18 months old. I put her on every ride in Magic Kingdom that didn't have a height requirement, and she LOVED it! The same applies to my son. I've also attached the
height requirements web page so you can look at the rides in each park.
Hollywood Studios has kid friendly rides and even more special performances to just sit and watch! Don't miss Beauty and The Beast-Live On Stage, or Disney Junior Live on Stage. That's just two out of many that your son will enjoy.
My son loved Animal Kingdom at that age (& still does - he's 10). There's so much to see; even real GORILLAS! Epcot is one of my favorites, and has rides that he can certainly ride, but if time is an issue, this is the park I would go to last. Teenagers and adults love it though.
I hope this helps! Your little prince will love the trip! If you have any other questions please let us know.