In Scandinavian folklore, a changeling—known in Norwegian as bytting, in Swedish as bortbyting, and in Danish as skifting—was believed to be a supernatural substitute left in place of a human child that had been secretly taken. The original child was thought to have been abducted by hidden beings, most commonly trolls, the hulderfolk (the “hidden people”), or other underground or nature-dwelling spirits. In some traditions, elves or similar entities were also blamed. These beings were believed to take healthy human infants for their own purposes—whether to strengthen their own kind, replace a weak offspring, or simply out of desire for human vitality—and leave one of their own in the cradle.

The period of greatest danger was considered to be before a child was baptised, reflecting the stron ...