You might want to ask specific questions pertaining to your son's situation on the Disability Board. They might be able to give you more detailed instructions.
http://www.flyertalk.com/forum/disability-travel-224/
By all means, ask for assistance if you feel it would help, and your right! On a technicality, the airport employee might have to assist your son directly, not just help all of you in general. You may want to prepare your son accordingly.
Your son might be very capable but please use worst-case scenario when answering any questions. Remember that when flying, your son might be tired, worn out and/or conditions might not be ideal, like outside air stairs or extra long distances.