Use 'Allways' iin Delhi, they will take care of you (for a fee) if you need special help. That said the arrival in DEL is rather calm, you have to walk a rather long open walkway to get to immigration and stand in line for a while depending on what nationality you are. Indians are not very sensitive to autistic children in particular but very understanding and accomodating for children.
Take a look at this section for more tips:
https://www.flyertalk.com/forum/travel-children-221/
https://www.flyertalk.com/forum/disability-travel-224/