I took a well-reviewed book back to the library today, having given up after reading maybe a quarter of it. I've come to the conclusion that I really don't care for books that involve a team doing spy work. (Or probably a team doing anything else.) I can't take the long, drawn out process of bringing the team together. I also think spy stories in which kids become some kind of secret agent for adults defy logic. Over the last couple of decades, our culture has been very, very big on teaching the young that strange adults who want you to do something dangerous and secretive--or just secretive, for that matter--are probably up to no good and to be avoided. So isn't the average kid reader going to wonder what's wrong with children who drop everything to become spies for some weird adult they've never seen before?
I've been thinking about this today, and I've decided that perhaps the best way to write a kids' spy book is to avoid using adults at all. Somehow, kids have to be the initiators of the action. Or you could set the story in an alternative world where kids aren't supposed to be protected they way they're supposed to be in ours.