Hello!
I am primarily a composer/music producer but I also provide voice acting and narration services, in both English, in which I'm fluent, and Portuguese, of which I'm a native speaker.
I believe my voice fits your description and is also more young sounding (but not juvenile sounding) which could be more appealing to your son. I can also modify my voice as to distinguish the books' different characters.
I would very much enjoy working on this project. Contact me in either English or Portuguese so we can discuss further details.