I think it's easy to teach love as long as the child's mind isn't sullied with hate. I think the difficult part is unraveling any pre-existing hatred and replacing it with love.
Kids aren't born hateful unless they're sociopathic or psychopathic, and even then not all sociopaths and/or psychopaths are violent. Any young bullies are a result of their parents ideologies and the environment they were raised in. The quote still stands that hatred is taught and love is not.