Book tickets and watch videos in advance. Because of the pandemic, most parks are requiring advanced booking. It's easy to do with Disney. Once you've picked your park and date, start watching videos of the different experiences/rides to help your child/children prepare and plan for what they'd like to do.
Upon entering the park, visit guest services to get the Disability Access Service. You have to let them know your child's diagnosis, and why they would struggle waiting in line. This pass is a game changer. You walk up to the ride or experience, let them know you have the DAS, they will scan your child's entrance pass and basically put you in line 'virtually'. You can then walk around, use the bathroom, visit the many sensory calming stations instead of waiting in line. When your time is up, walk back to the ride and you'll go through the faster lane and will not have to wait more than 5 minutes.
Don't force any experiences or rides. Let your child dictate what they are ready to try. Notice the early warning signs of a melt-down and take your child to somewhere calming for them.
Have lots of snacks. These parks can be overwhelming with lots of walking and sensory input. We were constantly stopping to grab a little snack all over the park. Epcot was perfect for Luca because he loves to try foods from all over the world, so we tried our best to get something from every country.
As a parent, make sure you are getting nutrients, water and rest. It can be a lot to navigate, but it can also be a really fun experience. Give yourself a deep breath, relax and know that your child will pick up on your energy. Enjoy, relax and take in all the memories being made.
Don't try to do it all. Disney World has 4 different parks. For us, it was a long journey to get there, and we talked about doing multiple parks, but decided that it would be too much for Luca. We choose Epcot Center, because it would be less crowded and it had rides Luca was interested in, plus food he was curious to try. We also took 2 days following to rest at the hotel, swim in the pool and go down to hotel water slide. Having the rest days was a great way to ensure that our vacation was fun and restful.