This product is for children 8 and up and even then children are not to use it without supervision. I bought it for my 5-year old and wouldn't leave her alone for even a minute while using the oven. When it's not in use it's in an upper cabinet and out of sight. She would never have the opportunity to put her hand inside the oven.
How frightening it must have been for this child to go through this and scary for the parents as well. HOWEVER, if the child had been supervised it would not have happened. There are many, many toys/games/activities children can play with that are dangerous when misused. If you give a 5 year old an oven with a slot in it, you imagine the worst and then make sure it doesn't happen by being a responsible adult and supervising.