We have a child with Asperger's that has similar issues. We have taken him to WDW many times, because it is one place where he can have many positive experiences. That being said, it can also be completely overwhelming, and not one of our trips have been "meltdown" free. Over the years we have gotten better at the pre-trip planning and preparation. We use storyboards, lots of pictures, daily schedules, etc to let him know what to expect. He looks forward to the trips. We ,as the family, try to get all the details nailed down. Rides, he was expecting, closed for renovation at the time of a visit, can be a big disappoinment. So, we check and double check, hope for the best, prepare for the worst (a meltdown) and have a crisis plan in place that the adults agree to before hand. We have found that with our guy, if we, as the adults, remain in control of the situation and calm, it helps to keep his anxiety in check. We have found that a DVD player with his favorites movies, a set of earphones, etc. can keep him in a "bubble" during transitions and check-in times, especially when he is tired. He uses these things to "destress". It might be useful for you to have available the calming strategies prior to checkin in case the process is prolonged.