Great mystery show for tweens and teens!
Pretty Little Liars is a fun mystery show full of suspense and drama and romance. My daughter watched it 3 years ago when she was 10 and loved it, it's her favourite show now. There is lots of lying (often to parents), some cheating, occasionally some excessive drinking, and one teen takes drugs (although you never see her taking them and she has to go to boot camp when her parents find out). HOWEVER, your kids don't copy what they see on TV! TV is for entertainment, past the age of 7 your kids don't need shows with "good messages". The only good message in PLL is loyalty, most of the stuff they do is kind of bad, but your kids won't copy them if they are responsible! Teens don't act like this in real life, it's all hammed up for the show so don't worry about your kids trying to be like the main characters. The only bit I might worry about is the teacher-student relationship. I think it's a good idea to talk to your kids about how this is illegal and wrong before they watch it. The show tries to lower the weirdness level by making the teacher only about 4 years older and they met before he became her teacher and it's the student who keeps saying they should stay together, but if you look at it as if it was real life it is still illegal and wrong. Halfway through Season 2 he stops being her teacher so it stops being weird luckily. But make sure to talk to your kid about how this is not okay, so that they don't get the wrong idea from the show. The rest of the stuff they already know.
VIOLENCE: There is much more suspense than violence (some scenes have lots of drama and suspense emphasized by scary music.) The main plot of the show involves a teenage girl's murder but you never see her body. A few dead bodies, but they are more eerie than scary. Barely any blood and no gore in the entire 7 seasons. Most dead bodies are just pale people lying on the ground with no blood, one is hung with a rope but you only see him after he has been hung and his face is very pink, that's all. Someone is stabbed (not fatally), some blood but no gore. At one point, in the almost pitch black, the sillhouette of a teenage boy's body lies on the floor next to an axe. The girls can't see (and you can't either) but it is suggested he has been decapitated. There is a dark roundish object at the bottom of the stairs that could be his head. It sounds much worse than it is - no gore whatsoever.
SEX: Lots of kissing and cuddling. Occasionally a guy is seen shirtless. "Sex" scenes never involve having sex. The couple kiss and cuddle a lot, make their way to the bed and lie in it kissing, and then the scene ends. In some of those scenes they take their tops off (the girl always has a modest bra or vest on, no real nudity) and while they are kissing the camera shows their backs or arms to give the impression they are about to have sex. Afterwards the characters reference that they had sex, but never anything explicit. Consent is almost always confirmed with "are you sure?" "I'm sure." One character is gay, this is referenced a lot while her semi-homophobic parents try to understand her coming out. In a flashback, we see that her best friend (the one who died) once took advantage of her sexuality and kissed her, before telling her she wasn't interested. She has girlfriends and ends up in a stable relationship with another girl in the last season, who becomes pregnant with their child. If you're not okay with one of the main characters being gay, you might not wish to show your children this show as it is very pro-LGBTQ (although, again, it won't turn your child gay if they see a gay girl on TV so if that's the issue then it's fine).
LANGUAGE: The word "bitch" is used pretty frequently, often by the girls to each other in a joking way (e.g "wake up, bitch"). "Ass," "damn," "hell," "oh my god" (as an exclamation) are also used, but the only swear word used is "bitch".
DRINKING/DRUGS/SMOKING: The girls sometimes drink a little at parties in the later seasons when they're old enough. Parents also drink a little at parties or events. At one point in the first season, one girl brings a flask of alcohol to a party when she is underage and her friend (also underage) drinks it all after a phone call with her long-distance girlfriend who she thinks might have moved on. She gets very drunk but regrets it in the morning. Sometimes characters drink excessively or get drunk but there are usually repercussions. A mother finds drugs in her daughter's girlfriend's bag and the girlfriend is sent to boot camp.
Overall this is a great show, and if your kids are responsible at all they will not copy the characters (although, again, probably remind them that the teacher-student relationship is wrong while he is still her teacher). I recommend it for 11+. If your child is clued up and okay about all the stuff in here they can probably watch it at 10, and if you are worried your child will get scared or grossed out by the kissing then best to leave it until they are 12 or 13.