answer:If it were the other way around, the four year old stabbing the eight year old, I would say the four year old didn’t know any better. Eight years old is old enough to understand the consequences of your actions. Why did the kid have a knife in the first place and why was he stabbing a doll with it? If he’s exhibiting behavior like this at eight I think he needs some time in a quiet place with a lot of doctors. I think the parents have some serious explaining to do.