Allan is a young boy who was kidnapped by the Alpha Vampire.
During the Winchesters meeting with the Alpha Vampire, Allan enters the room and tells him that Edgar is there before being dismissed by the Alpha Vampire. After Edgar's defeat, the Winchesters ask about Allan who the Alpha Vampire admits is the only child currently with him. At the Winchesters insistence, the Alpha Vampire has Emily help Allan get his coat and releases the boy into the Winchesters custody.
The Winchesters take Allan to the police who think that Sam and Dean kidnapped the boy, forcing them to escape out a window. While discussing their narrow escape, Sam notes that he doesn't care as long as Allan gets back to his parents.