I recently volunteered at GameCon, which is a convention for Junior High and High School kids in the Colorado Springs area. Last year a friend of mine volunteered and inspired me to put on a historical miniature game. The convention games are mainly card games (Magic), boardgames, and cosplay. I ended up being the only miniature game. I was surprised at this as I always see lots of 40K miniature games or other miniature games like X-Wing at other local gaming conventions.
Overall, this was a great convention for the kids. Most of the kids that joined in my game were really into playing the War of 1812 (Muskets and Tomahawks rules) 28mm skirmish game. This came as a big surprise. My take away is the kids that come to the convention are wanting to play anything. I would say they are less picky than older gamers going to game conventions. Some really got into my game and could have played it all day.
I just laid down terrain on the table and put out a number of miniatures based on how many kids were at the table. When kids would want to join, we would divide up the units or I'll pull more out. I ran 4 games on the table. Two were full table and two were just run on part of the table when there were only two players.
The kids picked up the rules pretty easily. I would recommend keeping the rules simple, something like Sword and the Flame. It was a mix of gamers, some really got into the game and a few were more interested in turning the rulers into drum sticks. I'd prefer the more focused kids, but I'm impressed at the interest level all day long. Not all kids stay for the whole game, so be ready to swap troops to new or existing players.
The gamers are from middle and high school, so be prepared for damages to terrain, mat and miniatures. I would recommend not bringing anything you do not want damaged. I didn't mind their handling and prepared myself mentally for damage. I don't mind touching up my miniatures or gluing some terrain back together. I ended up with no issues with damaged terrain. I have yet to check the miniatures, but I think they did okay.
I think all cities should do this at a high school at least once a year. It is a great way to introduce kids to the various types of gaming. Something other than video gaming.