Changeling

That the elves sometimes steal a child from its crib and leave one of their own in its place is old knowledge — whispered by grandmothers, half-believed by everyone, and confirmed often enough to keep the fear alive. No one knows why the elves do it. What's certain is that it happens across every station of life, from the wealthiest house to the poorest hovel, and that no family is ever quite the same after.

A changeling looks human as a child, but adolescence brings out something else — a sharpening of features, an otherness that can no longer be explained away. They reach adulthood around the same time a human would, then simply... stop aging the way people expect. Whether they're a race unto themselves or elf-spawn whose nature was stunted by growing up among humans, no one agrees. What's certain is the cost: few changelings are allowed to stay once the truth comes out. Some find a place at a witch's or wizard's side; most are left to make their own way — wandering, watchful, and rarely trusting the world enough to be at ease in it.