This wouldn't have happened with any of my kids because I wouldn't let it happen. Kids are inclined to kick because they're bored, naturally energetic and don't fit in the seats properly. The correct procedure is to address the parent. It is not appropriate to intimidate the child or even speak directly to him in a "non-threatening" manner. It is not appropriate to attempt to intimidate the parent. Rudeness in response to rudeness is still rudeness. If I could not get the parent to resolve the issue, I would ask a FA for assistance.