I recommend running "Gorgoldand's Gauntlet." The Gauntlet is available online somewhere, it's one of the best intro adventures ever, and it has a great balance between puzzles and fighting. Train 4 or 5 kids up on how to run it and make pre-generated 1st level characters.
That will teach them to play and hopefully ignite the spark. Teaching them to create characters can come later. There's lots of folks on here who have run it before (I've used it 5 times, and swear by it). Also, if you're there and another junior-GM runs into trouble, you can lean over and help out.