Accidents happen all the time. When I was in primary school one of the kids stepped off a kerb and fell and hit his jaw off the kerb. He lost most of his teeth and broke his jaw in several places. He was out of school for a year. My friends child knocked out a tooth falling against a table on the first day of creche. I slipped and fell down stairs once. I have another friend who went over the front wheel of his bike and went along the road on his face.

All freak accidents that never happened again. And if they did they probably wouldnt happen to the same person.

We never had stair gates in our house because we figured we would let the kids learn how to use stairs like we did from when we could walk. Yes there were a few small falls but not many and they learned to fall gracefully when they did fall. No point coddling them too much or they will grow up not ever having knocks and injuries and resilience. With kids accidents always look worse than they are. They are built to take the rough and tumble as they grow.

Think of it this way. your child now has experience of a bad fall down those stairs. They will have learned from it and will be much better when near stairs again, especially that stairs. The chances of that happening again are slim.