While this show doesn't have any educational value or life lessons at all, it is a very entertaining and lighthearted show. I started watching this show at age 7, about a year after its debut on Cartoon Network. Personally, I think the violence in the show is a bit much for kids under 6, iffy for 7, and ok above 8. While the human characters are hurt sometimes, put in the hospital on occasion, it's nothing that involves any blood or other violences. The girls wear low cut shirts, and are occasionally seen in undergarments, but that's all in terms of sexuality. This is a good entertainment show, and boys and girls alike should enjoy it.
Edit 8/23/11: Whoever said that Ulrich and Yumi have sex is wrong. They don't even kiss.