When i was 8 I liked books that were through and didn't try to hide things that some adult thought was too complicated for me.
So I had a tendency to read college level texts from my Dad's library.
Often, I encountered things that at first looked overwhelming, an example that comes to mind is solving resistor networks using determinants. Actually the more complicated, the more I was motivated to discover how it all worked, and there was always my dad to fall back on (even though he sometimes thought I was a pest).
With that in mind, I'd recommend:
http://interactivepython.org/courselib/s...index.html
I think your 8 YO will have fun.