We stopped by our house one day on the way to a show to pick up a forgotton jacket, pony on the trailer behind us. Our next door neighbor has a young daughter with Downs. I invited them to walk over and pet pony through the door while dd went inside to retrieve her jacket.
Pony, who was munching away from his hay net and usually mugs for treats a little given the opportunity, absolutely froze as soon as she put her hand on his face (even stopped chewing) and for the next ten minutes or so barely breathed and didn't move an inch while this little girl touched him all over his face and neck. I swear, he KNEW.
at the TR barn where i used to volunteer they had a little $#!$#@ of a pony who would do her best to bite, kick, stomp, or otherwise injure you--unless you were a small child, or had a disability. little kid trying to put her bridle on upside down? no problem. rider with CP yanking the reins? piece of cake. she would even stand there and doze as autistic kids had tantrums on her, ignoring flying fists and kicking feet.
but once someone adult, or "responsible for their actions" tried to tack/groom/lead/ride her, she'd try and take a chunk out of them.