The people who are most profoundly impacted by what they see, and are most strongly inclined to emulate it, are those who do not have strong moral standards to guide them and deep ties to the community around them. This is why our family culture is so, so important.
In the most practical terms, this means things like not allowing our children to see movies that are inappropriate for their age. It's really not until a child becomes a teenager that their brain is developed enough for abstract thought. That means that before that, they take what they see quite literally. That's why when a child sees a zombie movie, for instance, they are terrified by it: they really think there are zombies, and that they are coming to get them.
Of course in our day and age, our kid might just go to the neighbors and watch the movies there that we won't allow them to see at home. But again, if you've built openness and honesty into your family culture, this isn't as likely to happen. Your kids are more likely to tell you if it does, or at least initially show signs of distress at the dissonance they are experiencing that the parent who is paying attention will notice. Having these kinds of standards is not easy, to be sure, but that this is the kind of thing parenting is meant to be about. It will serve your child far better than trying to be hip and cool so you can be their friend.
Another important part of a healthy family culture is talking to your kids about what they are seeing. You can't shelter them from everything, nor do I think we'd want to if we could. Somewhere along the line they are going out into the world, and they'd best be prepared for that. Watching movies or televsion with them, playing video games, seeing the movies they are seeing, and using those as the basis of conversation are all great opportunities to talk about faith, values, and approach to life.
Additionally, the development of strong boundaries, close relationships, and the moral standards that keep them healthy, is one of the BIG reasons why I have found going to church is so, so important. It builds healthy ethical boundaries into the framework of our psyche and our lives. It establishes deep bonds of affection between us. I simply cannot overemphasize the importance of this.
It is also why part of the culture Jesus left us is not to just look after ourselves, but to reach out to the lost and lonely ,the disenfranchised and disturbed, and welcome them into our common life marked by love and acceptance. We are to actively look for such folks, notice them, and then seek to build relationships with them so they too will know that they are loved. We want to help them understand the positive impact each of us can have on the world, and how deeply satisfying making that difference can be.