Hi Jordan,
There is plenty to do for children (and adults) of all ages at Walt Disney World. I started bringing my own children to the parks when they were under two years old and we always felt like we had more than enough to do.
Ride participation is solely based on height, not age. Your little one can go on any ride for which there is no height requirement. This gives you many dozens of choices including Buzz Lightyear Space Ranger Spin, It's A Small World, Winnie the Pooh, Dumbo, Mad Tea Cups, Carousel, Mickey's Philharmagic, Peter Pan, Pirates of the Caribbean, Country Bear Jamboree, Haunted Mansion, character greetings, character meals, parades, and much, much more (and that's just at the Magic Kingdom).
Take a look at the
complete list of attractions at the parks. If there's no height requirement indicated, then you're welcome to enjoy it with your son. You can also bring him into any restaurant at Disney World (with the one exception of Victoria & Albert's). Disney is truly a place that works for everyone, regardless of age.
Good luck with your planning. Please let us know if you have additional questions.