Abdullah ibn Abbas:
When the children of a woman (in pre-Islamic days) did not survive, she took a vow on herself that if her child survives, she would convert it a Jew. When Banu an-Nadir were expelled (from Arabia), there were some children of the Ansar (Helpers) among them. They said: We shall not leave our children. So Allah the Exalted revealed; "Let there be no compulsion in religion. Truth stands out clear from error."
Abu Dawud said: Muqlat means a woman whose children do not survive.