Welcome to disABILITIES.
I have read posts from/talked with people who have used GACs (Guest Assistance Cards) for visual disabilities. Hopefully, you'll also get some first-hand information from people who have used them.
You are not required to have a doctor's note to get a GAC, just to be able to go with your son to Guest Services in any of the parks and explain what your needs are. The same GAC is valid for all parks and they are usually issued for the person with a disability plus up to 5 members of their party. The GAC is a tool that tells the CM what sort of assistance a person with an invisible disability needs. In your son's case, it would be to sit close to the front.
It's not an issue for rides, since each seat will have pretty much the smae view. The places where being in the front will be important for him would be live shows and theater presentations. Ask the CM at the attraction which direction you will need to be heading to get to the front of the theater once the doors open (most shows have a preshow or waiting area where you are sort of lined up before going into the theater). Sometimes it will be to the right and sometimes to the left. We have sometimes directed people which way to go when we have seen a white can since they were not told by a CM which way to go.
For theater presentations or audioanimatronic shows (like ITTBAB, Muppets 3D, American Adventure), the whole audience goes in at the same time and there usually are going to be some empty seats at the front because most people don't want to sit all the way in the front. There are a few shows (Little Mermaid is one) where every seat is often filled. For those, you might need assistance from the CM to get into the front row.
For the live shows (like Indiana Jones Stunt Show, Beauty and the Beast, Tarzan Rocks), there are some specific front seats designated for people with disabilities. The CM will show you to those.
Don't assume that you want to sit with the people in wheelchairs. For a lot of attractions, wheelchair and
ecv users sit in the very last row. We've experienced 2 "interesting" situations where people with visual disabilities got into arguments with CMs because the CM was telling them to go somewhere else and the guest were loudly defending their "right" to be with the "other people with disabilities". But they were not listening to the CM try to explain that the wheelchair users would be in the back row. So, sometimes, the worst place for someone with a visual disability to be is with the wheelchair users.
At American Adventure, you may want to ask to use the elevator that is used to take people with wheelchairs/ mobility problems up to the 2nd floor. That would be much easier (at least IMHO) than the usual way to get up, which involves going up an escalator or very steep set of stairs with a couple thousand other people going into the theater.