Hmmm... things don't kinda just bounce around in a car accident... they propell... fast. I have heard of children going through glass windows but have yet heard of a crush injury because of child wearing. I could be wrong though.
Actually, I have, where a child was being held by a parent and the belt was around both of them. The belt tensions back and the force of the accident pushes the adult forward, and the child is caught between the two.