I have always thought it was a wonderfully delightful way to introduce children to those sort of concepts. It was more EE/CE than coding (and the rest of the book was heavily ME), but I think the approach adapts to coding equally well.
(http://www.amazon.com/The-New-Way-Things-Work/dp/0395938473)
Also, libraries in general, including university libraries. Some books on homeschooling (such as Grace Llewellyn's _Teenage Liberation Handbook_) are full of pointers for self-study.
Haven't opened it in 20 years, but I don't think I've poured over a book the same way since.
https://www.amazon.com/Way-Things-Work-David-Macaulay/dp/039...
https://www.amazon.com/New-Way-Things-Work/dp/0395938473