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 strong influence of Christian belief layered over older folk traditions. Infants were thought to be particularly vulnerable when left unattended, especially at night, near doorways or windows, or in close proximity to forests, mountains, or burial mounds—places associated with supernatural presence. As a result, mothers were strongly warned never to leave their babies alone, even briefly.

Descriptions of changelings are strikingly consistent across Norway, Sweden, and Denmark. They were often said to appear physically unusual: sometimes unnaturally ugly, with large heads, thin limbs, or an oddly aged expression. Behaviourally, they might exhibit an insatiable appetite while failing to grow or thrive. Some cried incessantly, while others were eerily quiet and withdrawn. Developmental delays were commonly noted—they might not speak, walk, or respond as expected. In certain accounts, the changeling was believed to possess an old consciousness within its infant body, observing the world with unsettling awareness.