Ditto on what mbb said. We have an autistic 6 year old. We took him to WDW at 20 months, 4 years old and 6 years old. The best tip I can give is to get to the parks early, leave in the afternoon for a break, then return later if you want. We usually grab a fast pass for one of the kids favorite rides on our way out for the afternoon break. Then use the fastpass when we return in the evening. We never stay at the parks late either. We may return at around 5pm, then leave by 7pm. Short and sweet is better than comando with autistic children.
The stroller worked wonders on the lines when ds was having a bad moment. The stroller kept him calm. Just make sure you mention that you want to use the stroller in line when you get your GAC.
Have a great trip!