Great idea!
my dad got my brother and I building kits when I was about 4 or 5, so they feature heavily in my childhood. From building models I learnt not only how to follow instructions, but also how to work out solutions to problems (lost parts, screwed up decals etc.), and then of course building models leads to researching them and indirectly learning about history and geography. Not to mention skills such as painting, which leads to weathering/aging, and after a while you start modifying kits to make a version that isn't offered, which requires more research...all in all its a great way to learn many different skills that will serve you well throughout your life.
Love the early Revell boxart; check these out:

I really dig the PB4Y-1, I'd love to see a real one in that colour scheme, or even done up as a Coastal Command Liberator III or whatever they were called.
As far as kit costs go, yes new kits can be very expensive, but at my local hobby shop there are many decent older kits for cheap, especially if you don't have your heart set on a certain subject and are happy enough to shop the bargain rack. I remember seeing a nice Hasegawa 1/72 "Rita" for $15 recently.
Should also mention the Guillows flying models (the ones I could never get to fly); those add a whole other dimension to things:
http://www.guillow.com/cheers
greg v.