This is why. Rule number four people.
The individual who fired the rifle is responsible for every round that leaves the muzzle.
As a side note, it seems like there are more and more stories published in the news about the misuse of firearms lately. Maybe I'm just paranoid, but it's something I have noticed.
Update: Yup. Letting a three year old walk behind you with a rifle through the woods is bad policy. Fox news is chock full of shooting stories today.