This series takes story telling to a new level. It was originally suppose to be a mini series and the creators knew that. So they packed something into every line. You don't have to catch every line of dialogue to know what is going on though, but if your a fan of the old series, then you will wish that you will. The characters from Avatar the Last Airbender come back in the personalities and actions of their children. Korra may be the "great head strong heroine". So what? She is still a girl and a much more complex character than what most would make her out to be. Every line of dialogue has something to it.
So those are the good things and here come the things you should watch out for. Its staged in a 1920s era. Old cars, dirigibles and jazz. No drinking, but there are gangs who threaten shop keepers (of course Korra beats them up), but that is the least of the worries for parents. The main bad guy, Amon, is the basic embodiment of the spirit of communism. Talking about "equality" and fairness. Parents should discuss with their kids the dangers of those who preach "equality" and what equality is right and when it goes to far and becomes oppression on not just a minority but a majority.
Violence- The person who wrote the review above has not watched the full series. The bad guys use electric shocks hand to hand combat and at one point a water bender is bending the blood in some ones body to make them move like a puppet, it shows no blood but the sound the bending makes is kinda scary. Now this violence I could care less about since no one gets killed in front of the camera, but a little thinking would prove people do die. that I also could care less about. This is the type of violence without blood or gore, but obviously violence. It was well done by the creators so that it was not to violent for kids, but exciting for even adults.
Sex-not really. Mako and Asami kiss (he also kisses Korra or rather the other way around), but its not really anything to worry about. The relationships between the characters get complicated, so parents can discuss how people should deal with these thing in the real world.
Many characters are positive role models, but that can even extend to the bad guy Amon, who really seems like he just wants things to be fair.
Educational- There are historical figures represented by characters in the show. Hiroshi Sato represents Henry Ford for example. Amon represents a sort of Lenin, or Hitler. (good with words bad in actions) Parents can discuss these people with kids if they want.
Younger kids might not understand it completely, so they may get bored. Depends on the kid. My 6 year old sister watches it. :)
Its one of the best shows on any channel now days, with jokes and plot better than any show. Its awesome watch it. NOW!