There are worse than what I've written here, and worse things done. This is what they call the humans tricked into their families.
The Blessed: Mortal families chosen in any place the Fatas have nested. They are fortunate in wealth and health, and, after the age of seventeen, don't remember the pact they've made with the Fatas -- but, subconsciously, protect and aid them in the true world -- while the next generation is contacted and drawn into their world.
Changelings and Aislings: The ones stolen away. A fake body is left in the changeling's place, a thing made to look human, which usually dies, unless one of them is made to look like the stolen person. Aislings are humans frozen in place, made immortal, taken from their eras by any Fata powerful enough to accomplish this time-travel kidnapping.
Jacks and Jills: The Sluagh. The dead. Teenagers changed by the Fatas with a sort of alchemy of flower petals. They're assassins, keepsakes, hostages. The Fatas, the monsters, call this Stitchery. I call it Frankensteining.