One of our software engineers asked me today if I could recommend any educational material that he could use to train his kids in basic electronics. As far as I am concerned, the best material I have ever seen for young people comes from Forrest Mims. I highly recommend his web site, which also lists his publications. He also has some interesting astronomical work at this web site.
This material, along with some cheap prototyping hardware from Radio Shack, helped me train my kids. Some of Mims's books can be picked up at Radio Shack as well.
By the way, I also made my kids build their own PCs. This proved to be educational and fun.