I am not familiar with the introductory astronomy books, but anything from Filippenko can't be bad. I like
James Kaler's books, at least the ones I have.
Extreme Stars,
The Hundred Greatest Stars,
Stars, and
Cosmic Clouds are all books I have and like. They are not broad general astronomy books, as you can guess from the titles. But they are accessible to general readers, I think, and I am a fan of stars, so his books are a natural for me.
But something else comes to mind. It's not what you asked, but I think you should consider that astronomy is not just something to read about, but something to do. If you are not already involved with some amateur astronomy club or group, wherever you are, you & your son should be. In the
LAAS we have a 9 year old making his first telescope, and I know the Sidewalk Astronomers around here have had kids as young as 6 making telescopes. So astronomy can be just as "hands on" as it is "eyes on", and there is plenty of room for the young folks.