5e Setting Building: Changelings; both Fosterlings and Fetches

Come away, O, human child!
To the woods and waters wild
With a fairy hand in hand,
For the world's more full of weeping that

 you can understand.
- W. B. YEATS

The creatures of the Fey Realm have no children; they spring full formed into adulthood from the stuff of that realm. Many kith and many kin feel the generative instincts, which are frustrated by their very nature.

The result are the Fosterlings  and the Fetches

Fosterlings

Occationally a fey creature adopts a new born human child, taking them into the Fey Realm. The children are treated to lives of luxuary and wonder than no normal human child can ever hope for. Feed on magic and stories their entire youth, they mature into creatures indisputably fair and great talent. Each and every one has the potential to be a great hero or villain. However, this talent is almost always turned to the exploration of the hundred and one great tales of the the Fey Realm, where the fosterling may live a life of constant adventure, safe in the knowledge that nothing that they do not expect will ever happen, for it is in the nature of the Fey Realm to conform to the rules of stories, and for the fosterlings to be treated at their ultimately invulnerable protagonists.  For some the few however, these adventures hold little appeal. There is no risk of failure, nor truly any opportunity for the outcomes of them to be meaningful. So it is that some jaded fosterlings emerge into the material world, where they almost innevitably take it upon themselves to become wandering heroes or terrible villains  of some kind. They are almost always jaded creatures, soured on any earthly pleasure by a lifetime of wonders

Fosterlings are not only changed by their experiences. The very nature of the fey realm alters their morphology.  Their visage is shaped into an exagerated example of the way that a local culture describes beauty in their folk tales. Thought in almost all cases ears become elongated and pointed. They also tend toward Neoteny. Which gives their beauty an alien and uncomfortable quality.

Fetches

When the fey adopt human infants, it is often without the consent of the infants parents. Most fey who take children in this manner leave in the place of the child a fey construct, known as a fetch.

These creatures a small carved wooden dolls in the rough form of the child. They are animated with rough spun enchantments, and most last only a few weeks or months. This is not out of malice on the part of the fey, so much as their misunderstandings about the the material world.

A rare few, however, survive to maturity. They are forever other. Separate from the members of their community and intrinssically aware their nature is a secret. They often seem distant to those around them.