If you still have it, take the old GAC (Guest Assistance Card) and your child with you to Guest Services in any of the parks. Be prepared to explain to the CM what types of assistance you need/problems you expect. You don't need a long explanation or medical explanations. What you do need to be able to do is explain what types of things would cause problems and what sorts of assistance would be helpful.
The GAC is not meant to (and usually won't) provide immediate access or shorten/eliminate your wait in line. What it is meant to be is a tool to help CMs know what assistance you need, especially if there are invisible disabilities.
If you are going at a non-peak time, you may find that you really don't need the GAC much because the lines will be short. Using fastpass can also help a lot. Think of the GAC as insurance; good to have when needed, but not necessarily needed for each ride/show.
Have fun.