The first time we went to Disney World my son was 3 and he has high functioning autism, sensory processing disorder and ADHD. He gets easily overwhelmed by loud noises, bright lights... we came on that 1st trip because my husband had a work conference at Disney so it didn't cost us much money and I figured what the heck. But I honestly thought my son would hate it like he hated other carnival type places. Behold the power and magic of Disney! It was love at first sight! We were staying at Animal Kingdom Lodge and they gave us a Savanna view room, that right off was magical to him. Then the parks... he loved everything! Sure, some rides I have to put on his noise cancelling headphones for but over all for a kid who has meltdowns when I turn on the vacuum cleaner he tolerates that park noise pretty well. I never expected it to go as well as it did, the only meltdown he had was when it was time to go home and he tried to hide under the bed at the hotel and told us he was going to stay and live at Disney forever. We've come back a few times, we're coming back again next weekend, we went ahead and got annual passes on our last trip last month because we might as well... the kid is hooked.
He's also surprised me with how much he will engage with the characters. He's 5 now and he still thinks they are all real. He doesn't make a lot of eye contact with people but I've noticed he does look at the characters (even the human ones like Peter Pan) more in the eye than he does with everyone else. Again... Disney magic.