I'm 19 now, however my dad got me really interested in math when I was around that age. (Cs-ey math). He had this book on fortran which he told me to read before falling asleep as a way to get me to sleep by my bedtime.

It was a pretty profound book, and he used to always explain everything to me in terms of patterns and sequences, and could see if I could guess what lay ahead (in terms of a specific pattern or sequence). It was quite exciting when I got the answers right.

I would guess that a similar approach would work now, perhaps with a more modern language?

Also, kids (at least I know I used to) love stories on web security (admittedly the gritty details can be boring to them) however, with your expertise I'm sure you could find some way of conveying the excitement of beating the system without actually going into the details.

EDIT: To answer your question particularly about projects, I think that they will grow into coding from the more math-like perspective that I described. When they figure out algorithms and want to actually see them fleshed out in real results, they'll automatically take to coding things. After that, the world is their oyster.