Monitor what shows they watch: This is especially important for parents of very young children. There are multiple studies showing that media violence is unhealthy for children; there's never been a single study showing that it might be good for them.
Do not allow any child under the age of 8 to watch any show or movie that has appreciable violent content. Obviously, some small bits of violence are unavoidable, even in G-rated Disney movies, but that's where the next recommendation comes in...
Watch TV and movies with your kids: If you do, then they will be learning your values, not the program's. Discuss the content of the program with them. 'Why did someone punch someone else? Was that necessary? Is that what you would have done in a similar situation? This is called media literacy, or media education, and like sex education, drug education, or violence prevention education, it begins at home.
Become media literate: Media literacy is an extremely important concept. Many other countries have realized that children can be relatively 'protected' against harmful media effects by being taught about the media at a young age. In the United States, few schools have such programs. But that doesn't mean that you shouldn't begin the process by talking with your kids' teachers, counselors, or principals and asking, 'Why not?'
Keep the television out of the bedroom: For parents, controlling the media also means not allowing kids to have television sets in their own bedrooms. In one national survey, one-fourth of 2-5 year-olds, one-third of older children, and one-half of teens reported having a TV set in their bedroom. This is a prescription for disaster: How will total TV time be controlled? How can a child's choice of shows be monitored? How much co-viewing is likely to occur?
Conclusion
Know the media, control the media, and use the media wisely. In other words, teach your children well, especially when they are young, and you will reap rich benefits when they become teenagers or young adults.