Kelly,
I can't imagine a better place in the world (Walt Disney World, that is!) to take you son that the Magic Kingdom. If he is a fan of Mickey Mouse I would suggest that you bee-line to Toontown as soon as it opens in the late morning.
There are more things for a toddler to do in the Magic Kingdom than at any other park. Certainly it is more appropriate for him than Hollywood Studios or Epcot.
Now Animal Kingdom is a legitimate alternative. If your son has been to zoos, or is showing any interest in animals, this could be a great choice too. There are a lot of things to do and see there, and the animal viewing trails of the
Oasis Exhibits, the
Maharajah Jungle Trek, and the
Pangani Forest Exploration Trail are pretty impressive. The live bird shows and other theatrical shows are pretty great as well.
So if he is a HUGE animal fan, then go there, but otherwise I would rely on the kid-focused fun of the Magic Kingdom.
I am glad to answer any follow-up questions if you have any. Just ask me from my bio page.
Have a magical vacation!