First of all, Violence:
This show obviously about the "zombie apocalypse" and how it changes the world as we know it. The zombies, or walkers, in this show are more graphic and scary than most shows with similar topics, often having exposed bones and organs, missing limbs, and other gruesome features. It is a horror/thriller/suspense show, so this is understandable. Also, main characters in this show will get shot, bitten, killed, etc. It is important for parents or teens to know that this show has these often disturbing elements. I have been watching "The Walking Dead" since I was 12, right as it first aired in 2010. I personally don't mind the violence as much, however, most kids and teens are more affected by the violence. I think that it defiantly depends on the maturity of you or your children. If they are easily scared I wouldn't recommend this show to them.
The language in this show is a bit iffy, but i've heard worse from a few minutes in the middle or high school halls. The adults will often say things like: d-mn, h-ll, cr-p, etc. They do, however very rarely, use sh-t. They also have racist or other profane words such as: n-gg-r, p-ssy, and pr-ck. These moments are rare as well. I don't think that the language in this show is the main turn away for most and shouldn't be.
Personally, the only thing that I do not like about this show is the sex. I feel that it is not necessary and shouldn't be included. I wasn't really exposed to things like that before I watched the show, and it made me more cautious. To elaborate, the scenes in "The Walking Dead" that contain sexual content don't actually show any nudity or exposed body parts that would not be appropriate for kids, but often the women are topless, wearing only a bra, but it is completely covering any graphic or obscene parts of the body. However, there are scenes that parents should be wary of. In the first season of this show, on one of the first few episodes, there is a scene that includes sex, but I think that it is one of the most iffy scenes in the show. I would recommend that parents watch a few episodes before letting their kids watch it. Determining whether you want your children seeing this depends mostly on the maturity of your kid.
One more thing that I feel I should add that I think many other people are missing: The positive message. I feel that most people miss out on the point of "The Walking Dead". At least in my opinion, the show is about surviving despite all the odds against you, and being willing to lay down your life for others who mean a lot to you. It shows you that there is always something to live for, no matter how bad things seem. The struggles that all of the characters face on a daily basis seem more than most people could handle, but somehow they make it through the day. Their problems don't make them weaker, but quite the opposite; it forces them to become stronger and grow closer together despite their conflicts and differences. Their senses of what is right and wrong often become twisted and torn at by emotion, but most of them make the right choices. I think that these are all important lessons or a kid to learn, and "The Walking Dead" helps them. Most people just want to focus on the killing and sex in the storyline, but there is a lot more to it, you just have to look a bit deeper and you can see what I mean.