A changeling is a creature that was believed to be described as being the offspring of a Fairy, elf or other legendary creature that has been secretly left in the place of a human child. Sometimes the term is also used to refer to the child who was taken. The theme of the swapped child is common among medieval literature and reflects concern over infants thought to be afflicted with unexplained diseases, disorders, or developmental disabilities.
A human child might be taken due to many factors: to act as a servant, the love of a human child, or malice. Most often it was thought that fairies exchanged the children. In rare cases, the very elderly of the Fairy people would be exchanged in the place of a human baby, and then the old fairy could live in comfort, being coddled by its human parents. Simple charms, such as an inverted coat or open iron scissors left where the child sleeps, were thought to ward them off; other measures included a constant watch over the child.
It is said that changelings who forget they are not human and proceed to live a human life. Changelings which do not forget, however, in some stories return to their fairy family, possibly leaving the human family without warning. The human child that was taken may often stay with the fairy family forever.