It kind of depends if you will want to ride rides by yourself or only the rides that your son will/can. Choice A- You mix up the rides. A variety of adult rides and family rides. Choice B- "Dumbo-or-Die" where you ride every ride with your son.
Choice A- This will take longer than 2 days although if you get to the parks early, use Fastpass to the fullest, eat at off hours, and run to the most popular rides first, you should be pretty close to most of what you want to see.
Choice B- This will take around 1.5-2 days and should be more relaxed. Fit Fantasyland first and knock off Dumbo, Peter Pan, Alice in Wonderland, and Mr. Toad early. If characters are important, hit Toontown as soon as it opens(Ithink 1 hour after the park opens). Then take your time visiting the rides in Tomorrowland, Adventureland, Frotierland, ToonTown, and Critter Country. Rides in New Orleans Square are a toss-up depending on if your child is afraid of pirates or ghosts. California Adventure is much easier to decide what to do. FIrst hit Monster's Inc. and Turtle Talk, then the rides in A Bugs Land, then ride any Paradise Pier rides that interest your son and spend some time in the Redwood Creek Challenge Trail to tire him out!