As Tom has already mentioned, the Nottingham Young Gamers event took place a week or two ago, and I was fortunate enough to be one of the half dozen adults showing the youngsters the non-GW side of wargaming.
I was responsible for GMing a "Hadrian's Wall" skirmish game between Romans and Celts, and like any GM, I took four players at a time - two per team. Both rounds lasted about an hour, so the children had the chance to take part in more than one activity.
The game was played using my own quickplay ruleset Victory With Honour, which uses two scales for victory: tactical victory and Glory. The simple addition of a secondary victory mechanic sends most players nuts (in a good way) - especially children - and gets them fighting like their ancestors, with one eye on victory and the other on their reputation.
One round was a minor victory to the Celts and a moral victory to the Romans, and the other was a glorious Celtic victory. Watching the children scheme and pick their targets was great fun, as was hearing an eight year old say very seriously to his friend: "William, we have to start killing people now."
Anyhoo, here are lots of pictures of Mr Morris' lovely sub-Roman fortifications and the models he did up for his old school wargaming club.