There is not a pass that allows people to go to the front of the line (the exception would be children on Make A Wish or similar programs and people who are on mechanical life support like respirators).
They do have Guest Assistance Cards (we call them GACs here so we don't have to type out so much) which can provide things like being able to wait in a quieter, less hectic place, bring a stroller into line and have it treated as a wheelchair, avoid parts of lines that have steps. Each person's GAC might be different because even peopole with the same diagnosis have different types and levels of need.
Just having a child with ADHD doesn't necessarily mean a person needs a GAC. Some kids with ADHD will do just fine by using FastPass and going to the parks early. Others may need a GAC. During non-peak times when waits for most things are 20 minutes or less, a GAC might not really be necessary at all.
If you need more information, follow the link in my signature to the disABILITIES Board.
Edited to add: I got interupted while typing, so by the time I actually posted Mccall had also answered.