Heh, I actually started not on graphic novels, per say, but on the Sonic the Hedgehog comic book series. ^_^;; Which, though a bit corny, is actually still a totally fun series, you'd just have trouble getting at the copies number of back issues (though they did make a graphic novel compilation or two, which can be ordered). I then moved onto some lesser known graphic novels that, ironically, didn't really have words--the Age of Reptiles by Ricardo Delgado, which was a non-verbal, quite violent, but fun book of realistic dinosaurs, and the Gon series, a very cute series about a short dinosaur living in the modern wilderness defending his animal friends.
I then graduated to manga through Ranma 1/2 and Inu-Yasha, which hooked me forever and ever. Ranma 1/2 is romance/action/comedy, and is very funny--some of the humor is a bit dirty though (there's the occasional perverted panty thief), and there's brief nudity, but no real sexual content. Inu-Yasha has a lot of violence, and again some brief nudity (though not as much) and the occasional perv, but no real sex.
These days I read a lot heavier stuff--Sandman and Fables and Maus, etc. None of them are 'dirty', but they'll make reference to sex (and violence. lotsa violence), and are overall of a darker, more serious nature, and may be hard for a 10 year old to truly comprehend...depends on the kid though.
It's worth noting that, at Barnes & Noble at least, the graphic novels are actually often divided into several sections, based on age group. The bulk of graphic novels are located near the Sci-fi/Fantasy section, but then there's also often a small section for Teen Manga, and one in the kids department for young readers. these are very small sections by comparison, of course, but the books within are almost guarenteed to be clean, and there's some popular titles there. I know the kids section has comics based on the cartoons Avatar and Pokemon, and that they very recently released a volume of Warriors manga (Warriors is a very popular young readers
book series, about a group of warrior cats...hey, if you're lucky maybe the comic could be a gateway drug to the books

). I'd definately keep looking in the regular section too, because there's plenty of titles that are mature without having racy content.