The most common sense approach to preventing crime is to make sure that crime doesn't pay. In other words, make sure the punishment exceeds any possible benefit from committing the crime. Humans are rational creatures. When given a choice between an easy way and a hard way, we take the easy way.
Children learn from example.
They learn from what they see around them. A few years ago, in Washington, D.C., a teen-ager was shot at a local high school. The student charged with the offense was released into the custody of his mother. The next day, this student was back in school. The 500 other students at the high school learned a powerful lession that day.