From Our Catalog:
Let the Right One In (videorecording), 2008
Product description: Oscar, a 12-year-old fragile and bullied boy, finds love and revenge through Eli, a beautiful but peculiar girl he befriends, who moves into his building. When Oscar discovers that Eli is a vampire it does not deter his increasing feelings and confused emotions of a young adolescent. When Eli loses the man who protects and provides for her, and as suspicions are mounting from her neighbors and police, she must move on to stay alive. However, when Oscar faces his darkest hour, Eli returns to defend him the only way she can.
"Childhood's End: 'Let the Right One In' and Other Deaths of Innocence" gives an excellent overview of the role of children in horror (Free Library card login required to view).