Bare in mind that I am probably the worst teacher on the plant. Incapable of teaching a 9 year old the small multiplication tables....
An experience I'll never forget. Maximum fail.
Some people are innate teachers, others are not; there is nothing
fail about it.
Thing is, there is no need to treat this as a teaching opportunity at all. Let him observe and experiment; be a safety supervisor, not a teacher!
I wasn't much older when I started my woodworking hobby: one of my first ones was a hedgehog, having hammered a couple of hundred 4" nails about 1" deep into a small log.

(Fortunately, they were "reclaimed" nails from concrete moulding timbers, unreusable parts burned and me collected the nails from the ashes.)
Sometimes kids like to watch, sometimes to do; ask and listen. Talk to them like they were your colleagues (but omit jargon, and explain words and terms when they don't follow), and you have a friend for life. Probably make another engineer or scientist, though.
