[Daryl]

For those of us who have been smithing for a while, we sometimes lose our appreciation for the effort we have put in to achieve the results we now have. Crowd control is as much being polite as it is setting rules. I believe it has already been mentioned, place your previous, larger examples of your work slightly farther away from your forging station, trinkets and smaller items closer; have a photo album of other previous work handy; businees cards (especially important); if someone says their grandfather or whatever was a Blacksmith, ask them if they had the opportunity to learn anything or at least ask them if they would like to turn the blower for you.
Crowd control is not about corraling people like cattle, rather inviting and leading them to items and places mutually benficial.
I have never had a shortage of helpers or spectators. It has been rare when aggressive people or unruly children have been a problem; asking them to leave will offend no one else in the crowd. Some demos that I attend regularly have familiar faces, bringing along extra relatives or friends (this I value the most). I have had on occasion, people showing up later with items from their farm or whatever, either asking for it to be identified or on occasion wondering if I was interested in purchasing Grandpa's anvil, tongs or whatever; even had a couple items given to me (of course, you make them something in gratitude).
In the shop however, especially during public demonstrations, please do not allow parents to drop off their children so they can watch (read as you are now the babysitter). There is a difference between a young person being interested in what you do and actively watching, and some brat running amok in the shop. Inform those parents that any unruly children will be returned to their parents after being given three cans of Red Bull Cola, two packs of gum and one puppy!