Children of the Night

When the Philadelphia bank Eileen Townsend works for transfers her to Europe, she takes her sons (teen-age Chris and 10-year-old Max) to stay with her uncle Gustav Helsing. Gustav's passions in life are schnitzel, polka music and, we will come to find out, hunting Dracula, who is living nearby as businessman Alexander Lucard. Also living with Gustav is teen-age Sophie Metternich, who impresses Chris.
Max is also obsessed with vampires, and not knowing about Gustav's quest, he misreads several signs and becomes convinced that Gustav is a vampire. With his mother away on an assignment, Max goes to the only other adult he knows, the businessman his mother had introduced him to at a reception the previous day, Alexander Lucard.
At Lucard's urging, Max lures Chris and Sophie to Lucard's castle. Upon their arrival, Lucard reveals his true nature. Max and Chris get away, but Sophie is left in Dracula's clutches. Unable to reach Gustav, Chris and Max return to the castle to rescue Sophie.