[racket] Programming for 9 yo's

I would pick something very "physical" like robots, music, graphics, 3D 
printing...

Maybe combine the above with a Rasberry Pi or other exposed computer, so 
that the educational demo is not judged by the slick standards of some 
rather impressive laptops/tablets/smartphones/gameconsoles that they 
already see at home.

Or, take something they already know a bit, like a tablet, and show them 
that they can create their own things for it (rather than being passive 
consumers of something someone else has made).

If you want to do robots, and have a Roomba and a cable, you can always 
use "http://www.neilvandyke.org/racket-roomba/", though there is also 
non-Racket robot platform software that includes simulators with 3D 
graphics.

Or show them "http://scratch.mit.edu/" or "http://www.squeak.org/".

Neil V.