Parents aren't the only influence
As a parent you have an enormous influence on your child's values and behavior, but we mustn't underestimate the influence of peers and the media as well.
Excessive exposure to violence or disrespectful behavior can affect the way children resolve conflicts or treat others. The media can affect children's behavior directly, but it also influences kids indirectly through their peers' exposure to it.
Having an ongoing conversation
When your children are very young, get in the habit of talking with them about justice and other moral issues. Talk with them about violence and your feelings about it. By keeping the lines of communication open as they grow, you're providing your children with an invaluable opportunity to explore their own ideas about morality and to reinforce the values that are important to you and your family.
Life is full of moral decisions and quandaries. There are opportunities to talk about your family ethics and morality with your children everywhere. Use news stories, movies, TV shows, books, and daily life events as a platform for talking about moral issues.
Encourage your children, even at an early age, to express their own opinions, to think about what they might do and say in various situations, and to try to put themselves in the shoes of victims of injustice.