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.

Oskar is a bullied 12 year-old boy, longing to extract revenge on his tormentors but unable to build the courage to do it himself. But then he meets a girl called Eli, who gives him the strength he's been looking for. But Eli is not all she seems to be...