[Faceman]

The point is that you do not punish the child in this case. You do hurt him/her to avoid getting him/her hurt even more.
Crossing the red light in itself of course remains illegal. But the complete facts of the case (i.e. crossing the red light to save the child) makes it legal. No prosecutor would ever try to take up such a case (at least not in Austria) because the defendant clearly will be found "not guilty" (and not only by a jury in the US but also by written law like in Austria).