As a Parent myself, I have no problem buying manga for my daughter. Of course I censor them first, as she's 4 and doesnt need to see the adult side of things just yet. But She loves Kingdom Hearts, Warrior, Tinkerbell and a few others to death. And I dont mind it at all. It helps promote reading, which in turn will help her build a larger vocabulary and teach her to read bigger words. Plus its something we have in common; which I feel will help to build a better bond in the coming troublesome years of her youth.
Heres a few ideas outside of buying EVERY volume from borders/barnes & Noble (to help cut down on cost for those of you with pickier parents):
I belong to animetakeout (dot) com, which for those who don't know, its basically like blockbuster online but with anime and manga. I LOVE it! They have a very wide range of manga/anime to chose from. But you do have to be careful because some of them aren't marked and are yaoi/yuri.
Also, tokyopop does online free manga reading on their site every month. As well as preview reading for new books coming out. So you can get an idea of rather you want to purchase the book or not, without having to spend the moolah first.
And lastly, there are a few sites on the web where you can read manga for a low monthly price or just for free. But I would like to go on the record of saying that, though these sites are wonderful, you do not support the authors of the series by not purchasing the books and reading them online. And without the authors, we wouldnt have the manga that we all so love. That said, sometimes when your broke, you still need a manga fix. ^-~