DH bought DS an arduino starter kit for his 8th birthday a couple weeks ago. We've had a revolving door of visitors since then so he hasn't been able to start and I don't know much about it since it was DH's idea but perhaps it might be of interest. DS is beyond excited to get started with it. He is very math/science focused as well and has an insatiable thirst. He lives and dreams about designing robots....

http://www.arduino.cc/

I also recently came across a local Maker Junior group that we're going to try to check out soon. They have a few groups in various cities so maybe there is something close to you -
http://makerjunior.com/


Now off to search for some science fair experiments for pennies books - sounds awesome!