SiaSL, I love your idea about asking him about his "wierdest" reads - I've asked about his favorite/least favorite before, but never thought to ask about wierd, which I think would be a question he could really get into!
It is the best way I can think of to filter themes that a child might find disturbing in reading materials targeted to an older audience. Some will have less impact on a younger child, who will filter it all out, than on a teenager, who is more likely to get influenced by something that touches on themes that start being relevant to him/her. Reason why the group sex in Heinlein's _Stranger in a Strange Land_ at... 12? 13? was less of a problem for me than the promiscuous teenager (turned incestuous mother) in _To Sail Beyond the Sunset_ at 16 (yes, late Heinlein is *that* weird).
Also reason why all those dead/tortured kids bothered me a lot less as a teen than they do now that I am a mother
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If your son liked _Ender's Game_ look into the _Ender's Shadows_ series. I haven't read them yet (_Enfer's Game_ was a favorite, but _Xenocide_ was close to "hit the wall, do not open again" for me and I dropped the series, and the author) but people who persevered with Card liked it.
