Fuse #8 has asked for Manga titles for kids, "Manga on par with Babymouse."
The silence has been deafening.
I wish I could list title after title that I have discovered in my reading for the Cybils nominating committee for the graphic novels section. I haven't seen Hikaru No Go (main character is a sixth graders) or Yotsuba (sounds like a cutesy child Amelia Bedelia) but I will say that Kat & Mouse is quite a stretch for "KIDS (not teens)." The two main characters are seventh graders and the book features a two page spread overview of the Expensive East Coast Private School cafeteria that includes scores (Brains, Evil, Cool, Sports) for each of the cliques.
I poked around Google a bit and found MangaBlog on Manga4Kids, a site which reviews Manga for parents of children 13 and under, and gives feedback on plot, character & morality, violence, sexuality/body functions, language, and substances in each title.
But clearly, the publishing world needs to take note of this niche and get busy!