I have the honor of 'teaching' several LEGO camps during the summer.  The first camp was LEGO: Adventure.  I gave the kids several genre options to choose from, such as superheroes, western, gangsters, medieval and modern military, and then create games for them to play within the genre.  I use Minifigs for these scenarios, but often use third party accessories (weapons, armor, etc) to kit them out.  I've found that having a stock of generic Minifigs that I can outfit for whatever I need is essential.  I not only introduce many children to gaming, but they also get a chance for their imaginations to run wild!

Another thing I'll do is use collectible miniatures game maps for the scenarios' settings.  Basically, I have the kids build 3D versions of whatever is on the map.  Desks, chairs, walls...they and many other things are built and overlaid on the map.  I like to think they are 'LEGOfying' the game.  I then throw in my own home brew of rules and some custom dice and....Voila!  Instant action!

Below are some pics I took of games we played.  Essentially, the class chose superheroes and then a western shootout.  I didn't get too many pictures of the superhero slugfests, but I did manage one of Captain Marvel vs Superman (thanks Kenny).