Rabbi Tarfon used to take oaths, “May I bury my sons...” if something was not true. After his death, Rebbi traveled to his locale and asked if he had any sons left. They told Rebbi that the son of Rabbi Tarfon's daughter was alive, and that every harlot whose own price was two coins would hire him for eight. Rebbi said to him, “If you repent, I will give you my daughter in marriage.” He repented but did not marry her, so that people would not say that he repented just because of her.
Why did Rebbi go to such length to teach children of his friends? The one who teaches his fellow's son Torah merits to learn in the Heavenly Academy, and the one who teaches the son of an ignoramus can cancel decrees that God makes.