I think I was about thirteen when I started watching this?
It's very tame in violence, there are no swear words (there might be a few, but they are so rare I can only remember one).
While Mary isn't the best role model, she grows and matures to be a much better person. The youngest sister, and one of the maids, Anna, are incredibly lovely and someone you would definitely look up to. Mrs. Hughes, the housekeeper is every definition of a strong and capable woman. Edith, the middle sister can be spiteful but grows SO much over the seasons. Many other characters are positive as well, such as Patmore, Daisy, William...
There are positive messages as well-- the most recent episode was lovely, themed with friendship.
There is humor too, plenty of it. O'Brien and Thomas the Evil (or so they think) Ladies Maid and Footman are wonderfully. "I'll go fetch my button box," says O'Brien, looking as though that's some tremendous secret. It's truly hilarious (sometimes O'Brien is truly spiteful to someone, but most of the time, she's just a laugh and Thomas ALWAYS is. He'd never do something to really hurt a person)
It is beautifully filmed and the costumes are lovely. Each series spans interesting parts of history and usually has social issues (woman's rights, word war I (there is hardly any violence shown for that), the Irish movement, etc) which are good to learn and discuss. In the third season, we address Thomas's sexuality more, and the storyline is wonderfully well done, so there is always the difficulties of being gay, especially then to discuss.
Beloved characters do die, and one of the deaths, while not at all shocking by being gory or anything (none of the deaths are), is done in a traumatic way, because the person is in so much pain. But that's not until the 3rd season, and you will hopefully see it coming. Fellowes knows how to make us cry, though never showing anything.
The first, second, and third seasons are all very tame in terms of romance (it's really refreshing) . In the fourth season (massive spoilers ahead) there is a rape of a beloved character. NOTHING is shown, it is off screen, but the man does hit her on screen, and says some very creepy things later, and the aftermath leaves you with a shaky and sick feeling-- I'd say it was well done though, it wasn't just done for drama. But I'd skip over it and explain to your kids if they 14 and under (I'm 16 and left until it was over). In the first season, there is that corpse which has resulted from a man dying in character's bed-- in my opinion he forced her a little, though she never seems to think so. Something to keep in mind there, and point out to your kids, especially girls, that ANYTHING even as small as that counts as rape.
All in all, it's a very tame, very enjoyable and beautiful drama. I know I might not have made it sound that way, but when you put the fact you hardly see anything, and those moments are over 4 seasons of eight episodes, it's quite good. I'd highly recommend for family's to watch it together. ^__^ I adore it.