In case you are unfamiliar with the story, it goes like this: Ammon, Tamar's half brother was so infatuated with her he could think of nothing else. His friend, noticing his depression, asked him what was the matter. Ammon told him, and his friend came up with a plan. He told Ammon to pretend to be ill and when the king asked him what was wrong, he must say he was ill and could Tamar come over to his quarters and make some cakes for him.
Ammon did as his friend advised, David instructed Tamar to go over and bake the cakes for her brother and, you guessed, he raped her. The Bible goes on to say that Tamar begged Ammon not to send her away because she was now a disgraced woman. However, he now hated her more than he had loved her, and had her thrown out of his house. Read 2 Samuel 13: 1 - 20.
The Bible describes King David's reaction in a very short sentence: "When King David heard all this, he was furious" (v 21). In my Bible next to this verse I wrote, "And he did nothing."
The following verse reads, "Absalom never said a word to Amnon, either good or bad; he hated Amnon because he had disgraced his sister Tamar" (v 22).
David failed to deal with his son's wrongdoing and as a result Absalom (another son) killed Ammon, revolted against David and was later killed. David lost two sons because of his failure to act when his son did wrong.
Maybe David was very busy running the kingdom, but there is no record of him ever confronting Ammon about what he did, or having him apologize to his sister or try to make amends. He simply allowed Ammon to go his merry way, and suffered the consequences.
David is not the only father in the Bible who neglected to discipline the sons. Remember Eli, the priest? You can read about him and his sons in 1 Samuel 2: 12 - 26.
Parents, we must discipline our children in a way that fits their age and their wrongdoing. We can't brush things aside, hoping they would just resolve themselves. This is not the same as what I wrote earlier about leaving our children alone. You can read that post here. This is something that happened under David's roof, and affected two of his children. He should have got involved.
If we are unsure of how and when to discipline our children, tiny or grown, we can ask God to show us what to do, and He will.