From Time.com: How Not to Raise a Bully. (In short: teach empathy.)
Increasingly, neuroscientists, psychologists and educators believe that bullying and other kinds of violence can indeed be reduced by encouraging empathy at an early age. Over the past decade, research in empathy — the ability to put ourselves in another person’s shoes — has suggested that it is key, if not the key, to all human social interaction and morality.