BB guns are deadly weapons - especially these days. There are some very high-powered bb/pellet rifles that are used for hunting and could just as easily kill a person. Criminals that use bb/pellet guns in the commission of crimes are charged with the same crime as those that use firearms, due to most people would not know the difference.
I agree shooting a kid with a bb/pellet rifle would likely end your life as you know it, but depending on circumstances, might not result in as bad an outcome as one imagines here. Point being they are deadly weapons and can leave permanent injuries. The fact that the general public and these kids are this stupid is irrelevant to me. I would use any means available if someone pointed a bb/pellet gun or any other deadly weapon at me. With a kid, deadly force might not be necessary, but all situations vary. We have read about teens and younger killing people or other kids/babies.