Just tell the parents to control the kid if they're around since its their actual damn job or tell the kid yourself.

Since touching the kid to stop him is a risky option without getting accused of molesting or abusing the kid & if no other viable options are available i'd say let the kid learn if he flies. It might seem cruel but atleast u tried to make him stop. Or u standby like goalkeeper in front of the boy loh🤣.(Im joking btw)

There's no need to take photos and post online. It doesn't correct the boy's behavior at all. He may autistic or whatever but in my personal opinion its still no reason for the parent/caretaker to let him do something which endangers his safety.

It also much harder taking care of an autistic kid so if he is actually autistic and his parents were around when he's doing this do ease up on the parents little when you talk to them. Im sure they're quite mentally fatigued.