Is there any safety in the theory "it takes a village"? Discussion on minding your own business.

Dealing with a variety of people in this world, has me wondering. When I see a child in a place where I know they shouldn't be, late at night, should I inform the parent or let the family work it out themselves. The truth is, most people act like there children do no wrong. If you told a parent and they didn't believe you, you would lost a friend. Personally I couldn't keep a friend that doesn't believe me about their child's safety.