Hi Theresa,
While each of the parks offers many attractions for toddlers, I'm partial to the
Magic Kingdom for the best experience. When you think of Fantasyland which is tailored for little ones, some families can spend an entire day there alone. At the other "lands," there are many other attractions that entire families can enjoy as well as parades and fireworks.
And for something different, would your son need a haircut? He can actually get one at the Harmony Barber Shop! Click
here to learn more about that.
If you need a break during the day, you can easily hop on the monorail or water taxi to one of the nearby resorts (Contemporary, Polynesian, Grand Floridian) to do some exploring, shopping, or dining. We often did this when our sons were younger, and they will delighted to sit at the little kid areas in the lobby and watch Disney cartoons or have a chance to run around on the grounds.
If we can answer some more questions, please let us know!