I did a demo for a group of 9-10 year olds the other day and got schooled by a little girl.
When I do demos I like to make little twisty-handled butter knives/spreaders out of 3/8" bar. If I keep three irons in the fire at different stages of completion I can crank them out quickly, and no one gets bored. Of course, the last step is to cut the little knife off then quench it. After I do this (and make sure it's cold) I walk up to the group of kids and pass it around, take questions, etc.
Little Girl: Aren't you going to take that out?
Me: What? I'm sorry, I don't understand.
Little Girl: That (points to hot cut still in my anvil).
Me: Oh, uh, um, yeah. That's dangerous. Many smiths have injured themselves when they forgot to remove the hot cut from the hardy hole.
Little Girl: I know.
Me:
It turns out the kids had watched a blacksmith demo video a few weeks ago in class, and the smith in the video mentioned the dangers of leaving the hot cut in the anvil. I guess he made an impression on this particular girl!
Moral of the story: When doing a demo, think about your audience's safety first, but don't forget about your own safety too. After all, we're supposed to be teaching them the correct way smiths work.