I think Sardine probably runs a bit old for your kid. I've never really read one of the books straight through though.

>We only got through the first chapter last night, where Lex
>Luthor tries to steal Superman's powers, accidentally steals
>Krypto's instead, and starts exhibiting dog-like behavior.
>Which seems pretty sound, scientifically speaking. Also
>learned that the super pets can talk, but not around people,
>because it's their secret thing. This blew my son's mind.

The first rule about pet club is...

>I also picked up a random volume of Sardine in Outer Space
>because the title/cover was cool.
>
>And yo: You ever read a comic called Dungeon (Donjon in its
>native French)? It's mostly credited to Lewis Trondheim but
>Joann Sfar figures into the mix as well. I've recently heard
>good things but never read it before. Having trouble finding
>it on the library circuit.

I think I took a look for it when I first heard about it and couldn't find it and then gave up. *shrug*