I once saw a kid, about 3 or 4, standing up in a shopping cart, lean over the edge and fall out, do a 270 degree flip in the air and land on his back unharmed. (He was wearing a thick coat.) Things like this must happen extremely frequently and not always with such a happy ending.
I learned never to let kids stand up in a shopping cart.
I very nearly took a nurse apart for doing the same thing while checking my baby’s weight.
Luckily, I reached out and snatched her by the ankle before she hit the ground.