Let the Right One In (2008)

Eli is 12 years old. She's been 12 for over 200 years, and she just moved in next door.

When Oskar, a sensitive, bullied 12-year-old boy, meets his new neighbor, the mysterious and moody Eli, they strike up a friendship. Initially reserved with each other, Oskar and Eli slowly form a close bond, but it soon becomes apparent that she is no ordinary young girl.