A changeling is the child of a supernatural being that is switched for a human baby. The changeling appears in the folklore of many European countries, and references to the changeling may be found from time to time in modern popular culture. According to legend, fairies, trolls, and other creatures desire human babies either to raise as their own or to use as servants, and they secretly steal babies and replace them with their own offspring or a bewitched inanimate object. Human parents are said to be able to recognize the changeling by its ugliness or its odd or wicked behavior.
In medieval legend, tales of changelings are frequent. Some children were said to be particularly vulnerable: those not yet baptized, and those who were especially beautiful - often the blond-haired and blue-eyed. Male children were also said to be targeted more often.
There are a number of legendary precautions against changelings. Scandinavian lore suggests placing a steel item above the cradle of an unbaptised infant, while other traditions favor such practices as turning the infant's clothes inside-out or using amulets. In many cultures, the changeling is believed to be much wiser than a human baby, so it can be driven away by surprising it into talking and thereby blowing its cover. Methods for effecting this include cooking a meal in an eggshell or brewing beer in an acorn.
There are also a number of more disturbing methods for getting rid of a changeling that involve abusing the infant in various ways. Beating, drowning, and burning in a stove or in the fireplace have all been recommended as ways to deal with a changeling. A Swedish folktale tells of a woman who refuses to maltreat a changeling and eventually is reunited with her own child; the human child is healthy, and the woman learns that the troll mother who had her child had similarly refused entreaties to abuse the baby and that kindness had broken the spell.
Folklorists have two main theories about the possible origins of changeling myths. One possibility is that changeling stories are supernatural reinterpretations of an actual occurrence; populations forced into hiding by invaders may have exchanged their own children for the healthier ones of the invaders.
The other theory holds that infants with birth defects were the origin for changeling lore. This is consistent with the legend that male babies were more often replaced with changelings, as males have a higher incidence of birth defects. The infants in some changeling stories have characteristics similar to those that result from birth defects such as autism, progeria, or a number of physical deformities. Some supposed changeling cases may also have been instances of failure to thrive, a condition in which an infant does not grow or gain weight as expected and requires extra care.