Kids need to be taught not to play behind a moving vehicle, the same as they need to be taught not to stick their fingers in an electric socket. "Someone else's kids" who aren't being raised properly isn't enough of a reason to force people to own a particular kind of automobile (At least this was the predominant thinking before we lived in a nanny state).
A plan which makes small children responsible for preventing their own deaths at the hands of adults driving vehicles they personally chose seems at the very least unlikely to produce good results, assuming you are trying to keep children from dying. I suppose if your metric is “nanny state impositions prevented” rather than “children being crushed to death” then it could be considered a success.
