My ten year old nephew has expressed interest in model planes and tanks, and naturally I was happy to show him the ropes. He chose an 1/72 Airfix Curtiss Tomahawk as his first model and over a few sessions I showed him how to assemble and paint it. I gave him as little hands-on help as possible, pretty much just helping him with the decals and some small detail. He did good. Time will tell whether the hobby will stick but I can at least make the learning curve a bit easier. He was naturally a bit disappointed that it didn't turn out awesome right away, but luckily I still have my first model planes stored away. I brought him my very first model airplane (an Airfix Spitfire, of course) to show him that I wasn't any better when I started out, and that I was three years older than him at the time!
Damn, its been twenty years since I did that Spit. It looks like this hobby did stick with me..