I don't think the parents did anything wrong. They just simply wanted to keep the infant entertained by placing him in the washer for a few seconds while it was OFF, for the fun of it. No harm in that. How are they supposed to know that the door would seal itself shut and the machine would turn on? If they knew that, I'm sure they wouldn't put their child in. My home washing machine only turns on when I close it and press a additional ON button. Why doesn't that one have another button? Personally, I don't think I would have known either that the machine turns on immediately after you close the door.
And why can't the washing machine be turned off? Yes I understand that it needs to be sealed, but a emergency stop bottom wouldn't hurt. It should be there for other reasons too, like if you leave something important in the pockets of one of the clothes. A emergency stop button could also prevent future incidents with infants.
EDIT: As it is technically the parents fault for putting the child in the machine which your technically not supposed to do, I can't help but notice the failure in those machines by not implementing any additional control inputs. A powerful commercial machine should always have a emergency stop, or additional control barriers like the implementation of a final START button for the cycle. That is poor design.