I have a friend with a large family all born close together (8 DCs).
The second oldest has some lifelong medical challenges and also SN.
She is an energetic and very hands on mum, owns a large vehicle, and took the whole lot of them to lots of places beach, museums, funfairs, you name it when they were all small, often while hugely pregnant or with a very small baby in tow as well as all the others, like steps of the stairs. She is no shrinking violet, and very capable. She was a gym teacher and personal coach before deciding to do SAHM, so well able for the physical challenge.
She got very tired of the negative remarks about the large family, but just blew them off.
The ones that got to here however, were the comments about her child with SN, the behaviour, loudness, occasional tantrum, messy eating, lack of appreciation of other people's personal space, etc, and in particular about the fact that she ended up carrying this child quite frequently.
Instead of trying to talk to people over and over, she tried just ignoring them, but some people are incredibly rude and would attempt to talk to the child very critically, assuming they could be understood. She took to carrying with her a few cards, like business cards only twice the dimension and folded over, which she would hand out to people without a word if they criticised or challenged or questioned.
They began "Thank you for your interest in my child who has X condition" and went on to list some of the symptoms of the condition in general and refer to further information (a few websites and a medical textbook).
It worked really well.