A more thorough explanation:

The tender-years doctrine is a legal principle in family law that suggests that custody of young children, usually five years of age or younger, should be awarded to the mother in a divorce unless she is found to be unfit.

For example, if a couple with a three-year-old child gets divorced, the court may award custody to the mother based on the belief that young children need their mother's care and nurturing.

However, this doctrine has been rejected in most states and replaced by a presumption of joint custody, which means that both parents have equal rights and responsibilities in raising their children after a divorce.

Overall, the tender-years doctrine reflects the traditional gender roles and stereotypes that assume women are better caregivers for young children. But as society has evolved, so has the law, recognizing that both parents can provide love, support, and care for their children regardless of gender.