8 Simple Rules is a sitcom that is definitely aimed at pre-teens and teens, but it is still something that even kids can enjoy. But, the show does focus more on mature topics/issues that affect teenagers such as virginity and partying. Underage drinking is implied, so is sex. There are also many references to sex and sex jokes but most of them aren't obvious and kids probably won't understand them anyways. However, there is an episode in which the mom teaches a sex ed class at school and it many be awkward/inappropriate for some, especially the younger ones. As far as language goes, there are minor swears and insults (jerk, stupid, etc.) so it's nothing too bad.
The show is great because there are morals behind every episode. Not only that but it's just exceptionally funny and the acting is pretty good as well.