Our DS is now 12, with ADHD and SPD, and our first trip was when he was 8. Before our first trip, I really over-planned for every possible scenario that could happen. And I am so glad I did!
We watched YouTube videos of every ride and attraction that could be considered dark and/or scary. Over and over and over (he also has OCD, LOL!) . I used very detailed touring plans and followed them strictly. He helped to make the plans with me. If we got to an attraction, and he was afraid, I took my lead from him. I didn't force him to go on anything he didn't want to do. I gently encouraged, and sometimes he was brave and surprised me. I always let him know where we were going next.
We did get a GAC and used it mostly at shows so we could sit near an exit door. This helped to relieve a lot of anxiety, especially at shows like Festival of the Lion King and Indiana Jones. He was very antsy waiting for the shows to begin, but pushed through it, and was able to stay for the whole show. His first ride at WDW was Pirates, and he was very scared to get in the boat. I asked the CM if he could use my penlight so it wouldn't be too dark, and they said yes, and even gave us our own boat! He was scared but went for it! And he will never forget the CM saying at the end of the ride, "Yo ho, yo ho, get out!"
I think the thing that helped the most was getting into pin trading. We trade for Hidden Mickey pins and try to collect all the pins for the current year. We come with a list and set some goals, and spend a lot of time interacting with CMs as we move from one attraction to the next. He practices his social skills and has fun at the same time. We never get bored, and have a fantastic pin collection. We work together and share our pins!
So now we are heading back to WDW for our 8th trip in 4 years! He is now a pro! He has ridden every thrill ride in the park, including Tower of Terror, Expedition Everest, and Rockin Rollercoaster! He's been in the parade at Festival of the Lion King. And he's been the Jr. Director at Indiana Jones, introducing the show saying, "Lights, camera, action," to that huge stadium audience!
I think that WDW has been extremely therapeutic for our son. He has overcome so many fears and anxieties, and it has carried over into daily life! And we've had so much fun every visit! Every kid is different, with different challenges. If you let your kid take the lead and put your must-dos aside if necessary, it can lead to many fantastic experiences! Have fun!