HarperCollins describes Otto Undercover Born to Drive as being for ages 7 to 11. The cover of the far more sophisticated Shredderman Secret Identity says its reading level is 3.1, meaning, I'm guessing kids around 7 to 8 years old. And the lovely Ivy and Bean is supposed to be for ages 6 to 10.
Assigning age and grade levels is an imprecise science. You're going to find some wide variation in materials directed toward the same pool of kids.
Shredderman Secret Identity by Wendelin Van Draanen is a better quality book for younger readers than some of the others I've sampled this summer. Shredderman is the secret identity taken on by geeky Nolan Byrd in his campaign against bully Bubba Bixby. One could argue that we're dealing with a number of stereotypical characters here--the nerd, the bully, the hippy teacher. Or are they archetypes? I'll have to do some study on that subject. Kids, who haven't read as much as I have and may not yet be aware of stereotypes, probably won't care one way or the other. The bully really is unpleasant and Nolan really does try to do something about him in a real story.
Ivy and Bean by Annie Barrows is a charming and witty tale about two kids meeting. Is this a stereotypical situation or archetypical? Again, I must think about this. But, either way, Ivy and Bean is about two kids who are perfect for each other even though they, themselves, have to be convinced.
Both Shredderman Secret Identity and Ivy and Bean are the first books in series.