I agree that mom was negligent, but what kind of washing machine in a public place has no emergency stop and no way to open it while running.
Even shop tools intended for use by trained adults have emergency stop buttons.
I'm on the fence on this one. I say award some money to mom, and then hang her for criminal neglect.
The manufacturer is responsible by not having an emergency shut off switch on the machine.
IMO, the mother is responsible for none of this, except for the fact she obviously has an idiot for a son.