The main plot shows good characters and positive role models over all. Characters are shown making mistakes and coping with the consequences in a suitable fashion. I have enjoyed this show since I was eleven, and I think that it is an okay show to watch if you're a MATURE tween. If not, probably wait until high school age.
There are some mentions of beer/alcohol, an underage teen goes to a club with her older sister, and a thirteen year old has three tequila poppers in one episode. Sexual references are frequent (though mostly mild, and would go over children's heads) and one character has a son when she is seventeen, although is able to adequately raise him with the help of her family. The language is also iffy sometimes, several uses of "Son of a b!tch, SOB, damn, hell, crap and suck" as well as some implied swearing with clever noise cover ups in the background.
Overall, this show shows the importance of family with good role models, great morals and isn't something that you should be worried about your teen watching.