Interesting the conclusions you jump to. This is not about adults killing youngsters. It is about adults against adults--adults in the same family, trying to tear each other down, with words and any other means. Are you familiar with any other stories/myths of the time? You wouldn't have to research too deeply to discover stories of (grown) children killing and maiming their fathers. Maybe if it was phrased in Commandment form? Children, when you are grown, you shall not defame, injure, or kill your parents to gain their power, position, possessions.
Also, the penalty attached to many situations in Biblical times is/was to let the people know just how serious certain behaviors are.