What is a changeling in fantasy lore?

What is a changeling?
Today's post is the first in a series covering various aspects of SANYARE, especially the world-building and character development. I thought some of you might find it interesting to discover more about the book through the research I've done. If you have questions or suggestions for future topics, please let me know!

Changeling...human baby kidnapped by faerie

The protagonist in SANYARE is Nuriel "Rie" Lhethannien, a human changeling who serves as a messenger to the High Court of elves in the Upper Realm. She's human, which we should all be able to comprehend (I hope, anyway.  If you're not human, I'd love to talk to you.) but what is a changeling?

Hint: I'm not talking about Odo from Star Trek, who could morph himself into anything or anyone he wanted.

According to Wikipedia (the all knowing, all seeing, dictionary of the gods),

A changeling is a creature found in folklore and folk religion. It is typically described as being the offspring of a fairy, troll, 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 apparent changeling could also be a stock or fetch, an enchanted piece of wood that would soon appear to grow sick and die. 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. Some Norwegian tales tell that the change was made to prevent inbreeding: to give trolls and humans new blood, humans were given children with enormous strength as a reward.

As you might imagine, most of the changeling tales are told from the perspective of the concerned parents, who discover their child wasting away, sick and not getting better. In the stories, these parents are encouraged to trick the changeling into revealing itself, and then kill or abandon it to retrieve their real child.

The Glengarry Fairy James MacDougall, Folk Tales and Fairy Lore in Gaelic and English Compiled by D. L. Ashliman, University of Pittsburgh

There once lived in Glengarry a widow with a young child who was a boy. One day she went to the well for water; and when she was returning to the house, she heard the child, whom she had left sleeping quietly in the cradle, screaming as if he were in great pain. She hastened in, a gave him a drink as quickly as she could. This quieted him for a little while, but he soon broke out again as badly as ever. She gave him another drink; and while he was at her breast she looked at him and saw that he had two teeth in his mouth, each more than an inch long, and that his face was as old and withered as any face she had ever seen. She said to herself: "Now I am undone, but I will keep quiet until I see what will come of this."

Next day she lifted the lad in her arms, put a shawl about him, and went away as though she was going to the next farm with him. A bug burn ran across her path, and when she was going over the ford, the creature put his head out of the shawl and said: "Many a big fold have I seen on the banks of this stream!"

The woman did not wait to hear more of his history, but threw him into a deep pool below the ford, where he lay for a while, tumbling about and reviling her, and saying if he had known beforehand the trick she was going to play him, he would have shown her another.

She then heard a sound like that of a flock of birds flying about her, but saw nothing until she looked at her feet, and there beheld her own child with his bones as bare as the tongs. She took him home with her, and he got gradually better, and was at last as healthy as any other child.

But why would the faeries - the elves - want a human child? What could possibly draw their interest?

Some of the stories tell that young men and women are taken as lovers and used as breeding stock, sometimes living forever in faerie. Other stories indicate that the kidnapped humans are used as servants and slaves; skilled craftsmen and musicians taken for their abilities, men taken for their strength and used in battle, and women taken to act as nannies, nursemaids, or midwives to the faerie ladies.  These victims may be returned to their homes after their service concludes, unaware that more time has passed than they experienced in faerie.

Touching the Elements Shetland Islands Compiled by D. L. Ashliman, University of Pittsburgh

A fiddler belonging to Yell was waylaid and carried off by the trows while on his way to supply music to a Halloween gathering that was being held in a neighboring district. After playing for some considerable time he was allowed to depart, and immediately proceeded homewards. When he came to his house, however, he saw with amazement that the roof was off, the walls decayed and crumbling into ruins, and the floor grown over with rank grass. He questioned the neighbors, but they were utter strangers to him and could cast no glimmer of light on the remarkable situation. The place had been in that ruinous condition all their time, they said. He sought out the oldest inhabitant, but even he had no recollection of anyone staying in the place, but he did remember hearing a tale to the effect that at one time the guidman [master] of that house had mysteriously disappeared, and never returned. It was commonly supposed that the hill-folk had taken him.

The fiddler, of course, knew no one, and had nowhere to go, and when the old man asked him to spend the night at his house, he very gladly accepted the invitation. It so happened that the following day was Sacrament Sunday, and they both went to church. The fiddler asked to be permitted to communicate. This request was granted, but no sooner did he touch the "elements" [bread and wine of the Eucharist] than he crumbled into dust.

The last reason a human might be taken, some say, is that the faeries owe a tithe to the devil every seven years, and will sacrifice a human to save their own. They take what they want, under the theory, "All that's yours is mine, and all that's mine is my own."

My Twist on the Lore:

For my purposes, changelings are humans kidnapped by faeries and taken into any of the faerie realms.  In the Upper Realm, where Rie was raised, they are sold as slaves and servants, or act as foster children to elvish couples unable to conceive. In the "modern era", the fae will usually select orphaned babies, homeless adults, or runaway children that won't be missed, so as not to draw attention to the disappearances -- science has made the use of wood stocks impractical.

The selected changelings will age and behave as normal, unless or until they reach adulthood, at which point they no longer physically change so long as they stay in the magical realms. However, if they stay in the human world past sundown, their bodies will decay overnight to their chronological human age. They are treated as third-class citizens by society as a whole, unable to receive formal education and relegated to menial jobs once they reach adulthood.

What other changeling myths have you heard? I'd love to hear from you in the comments!