This ought to scare us. But that is the same kind of word gymnastics that Jesus condemned the Pharisees for. Jesus is saying that we are guilty before God for a heart that lashes out in anger and venom. Whether or not a person's life is terminated as a result is not the point. Unfortunately, this children's chant is false.
Words do hurt.
Anger, and the vile venom it inspires, kill the spirit. And those who spew this acid on those about them are not free from judgment. The God who condemns murder also condemns angry insult, for the both come from the same root. Man looks on the exterior, the action, but God examines the heart. And in the heart is the root of murder.