"That happens." "You're OK."
When kids are little, they don't know what matters. They look to adults to know how to respond.
When your kid falls, unless they're hurt, you say, "You're OK," dust them off, and send them back to play. If you fuss, they'll fuss.
If they break something accidentally, you teach them how to clean it up, and you say, "That happens. You'll be more careful next time." It's just an accident.
You can see the parents getting this right. Their kids are confident.