"It takes a village" is, I believe, short for a common saying, "It takes a village to raise a child" meaning children are best raised in an environment where more than just the parents are involved. A supportive community (teachers, other parents, friends, family) all contribute to raise a child. I have also heard it used in a more negative context. "It takes a village" could also mean that for every person that is guilty of some crime or bad act, others could be involved or at least could be supportive of that bad act.

It takes a village... The full expression is: "It takes a village to raise a child." In other words, it is important to have a strong community.