If your son is 7 to 12 years old and you want to get him started thinking about philosophy, I'd highly recommend he read these three books:

Harry Stottlemeier's Discovery (free PDF at the top right of this page: https://eric.ed.gov/?id=ED103298)

Sophie's World: https://www.amazon.com/Sophies-World-History-Philosophy-Clas...

The Fallacy Detective: https://www.amazon.com/Fallacy-Detective-Thirty-Eight-Recogn...

These books would provide a better introduction to philosophy in general, than reading about random topics in philosophy.

Sophie's World

https://en.wikipedia.org/wiki/Sophie%27s_World

https://www.amazon.com/gp/aw/d/0374530718/

https://www.amazon.com/Sophies-World-History-Philosophy-Clas...

Philosophy has a really strong "begat" narrative that helps if you're interested in learning the bases. E.g. A begat B begat C...

Also, I think one of the difficulties in talking about philosophy is that specialized language in the field has incredible compression efficiency. It's a lot easier to say Kantian than to take 1,000 words to recap his arguments and beliefs.

Study philosophy from it's base principles. Start with pre-socratic philosophers and keep reading until you get to modern day.

The book "Sophie's World" does a great intro here and it a really great weekend read.

http://www.amazon.com/Sophies-World-History-Philosophy-Class...