My vote... NOT to manga! For those of you unaware or just not fully informed on what it is, manga is basically Japan's version of comic books. This is different from the graphic novel. I see graphic novels more as a story told through illustrations. I don't mind comics; I grew up reading them in the paper or the Garfield books. But the Japanese version known as manga has taken it a little too far.
I know, I know, kids love the stuff. And I also know that as a librarian, I want kids reading. I order books about bodily functions and magazines if it'll get kids reading. So for me to lean toward the no side means something. By all means, make your own decision, but please, please, please... review these books very carefully before letting your kids read them. There's a review site No Flying, No Tights that has reviews of different series. But go further. Skim through them. There are a few exceptions (Naruto, I believe is fairly safe.), but in large part, manga features characters in skin tight outfits running around doing who knows what. Before I took over collection development for the youth departments, the previous staff worker ordering young adult bought a lot of manga. She bought a series that "had good reviews"... turns out it's about a young girl turned into a sex slave and the pictures were very risque, who cares if they're illustrated and not "real". The director decided to put them on the shelves since we had purchased them and once we made the decision to order it, she didn't want to censor them.
I see young children back at the manga shelf, skimming through the books because the format is legitimately appealing, especially to a reluctant reader. It makes me cringe when they're anywhere near this particular series. If you want my professional advice, this is one genre I could do without. But make your own decision.