Welcome.
I'm sure teri will be along soon. She has some good links to previous info from the disABILITIES Board, including info about Guest Assistance Cards (GAC).
You can go to Guest Services in any of the parks to request a GAC. The GAC isn't meant to (and usually doesn't) shorten your time in line, but you will be allowed to wait in a more appropriate place for your child's needs. When you go to Guest Services, be ready to explain what type of assistance would be useful to you. In your case, you may not want to wait in line with other people during cold and flu season.
If you will need any special equipment during the day or any procedures you need to do, like postural drainage, there is a First Aid station in each park. The staff are friendly and it is quiet with individual cubicles with cots and a chair. Medication that needs refrigeration can be stored at First Aid.