Not as good idea as it sounds...
At 8 or 10 you may be able to follow a simple radio circuit and get it to work, but there is no way any but the most gifted is going to be able to design one - it's just join-the-dots-with-a-soldering-iron!
I would expect that an intelligent 8 or 10 year old could grasp the basics of programming in many of the simpler systems and write their own code from scratch.