My son is 13 and also has Autism. We have been to DW 3 times so far. Things that have worked for us are:
1) Planning! Get a plan set with your ADR's, QS choices, Park choices based on crowd level, transportation choices, and daily schedule prior to the trip. There will definately be changes which will come but at least you have a framework of the optimum plan for your families needs. Teach your nephew coping skills for changes to a plan. Most likely his school will have options they can offer and work on prior to the trip. Social stories can be helpful. Or practice this in other environments prior to trip.
2) Get a
DAS card and combine with using FP+.
3) As already suggested, the noise canceling earphones are a must. Or you can use earphones with an ipod or phone with music downloads. It will block out sound and provide a calming tool for your nephew,if he enjoys music.
4) Fidgets, to use for long waits for a line, show, parade or bus ride after a long park day are essential! Book, electronics, hand held game, deck of cards, hand fidgets for sensory input (putty, magnetic pieces etc). Whatever is calming and distracting from a wait for your nephew. They have various plastic pouches sold on line for items you worry about getting wet.
5) As suggested before, go on you tube and have your nephew see ride videos to give him an idea of what to expect. Also have him look at maps of the parks and hotel found online to give him an idea of what the park will look like. You can even print them out for him to have for trip.
6) Plan on early morning (less crowded) arrivals and afternoon breaks for your nephew. Most people who have Autism can not handle long periods of over stimulation, which is what you experience in the parks. For my son 2 hours is the max that he can handle in a park and then he has to leave. We found either a nap or swimming in the afternoon is the perfect break before heading back to park in the evening.
7) If going to be at DW during hotter time of year definately make sure to check out cooling recomendations from DIS.
8) Have a plan for what you are going to do if there is a meltdown. Who is the person to handle the melt down, if he has to leave, what will be the plan for the rest of you. Sometimes you can manage the meltdown and other times you will have to leave. Having a plan ahead of time helps this very difficult challenge.
9) If needed make sure he has an id card on him with contact info in case he gets lost. Also, have a meeting spot he knows of or a plan of what to do if get seperated.
10) Avoid disney Quest! That place is sensory overload. my son had the biggest meltdown there. Most of my friends who have had their children with Autism go, regretted it!!!
11) Make sure to get meals and snacks in! Being hungry can lead to a melt down. Plan ahead of time what times you will be having breakfast, lunch and dinner.
12) Have Fun! Dont go expecting to see everything just go with the flow. Good luck.