It's a cart, not a racecar. Why would I be moving fast enough that I would have to jerk the cart to stop? You simply slow to a stop & address their behavior. It's not like you're running through the aisles at top speed. I'm calm enough not to feel I have to jerk the cart around.
Slowing to a stop might take a fraction too much time. I think it is irresponsible to not address the matter immediately. Toddlers are awfully unsteady on their feet.