What kind of parents allow a toddler to do this?
Parents who take their eyes off them for 10 seconds. In other words, every parent.
If you look away from some toddlers even for seconds, they can get up to absolute mischief.
My child, at NINE MONTHS tried to crawl down a flight of a dozen wooden stairs and ended up rolling from top to bottom. I had just unlatched the baby gate and was leaning over to pick him up and carry him down when he made his daring move. He rolled sideways like a hot dog and never lost consciousness—barely even cried when he plomphed on the landing; whereas I had screamed his name so plaintively my sleeping husband bolted up and fairly levitated down to him in a millisecond, and our next-door granny let herself in with her key! We are lucky there was no brain damage (he now has advanced degrees and works in NatSec). God is good.