I worked in a grocery store when I was 16 and saw too many clueless parents trying to Darwin their kids by allowing them to stand in the cart. The sound of a child's head hitting the floor is awful...and then the screaming afterward...
In the 70's they had "Paddle Talk," I believe it was called. Basically, a ping-pong paddle with messages on paper that one could flip to find the right message for the moment and then show it to the driver next to them.