Goosebumps was a kids television series which aired from 1995 to 1998 on the Fox network. Based on the kids horror books by author R.L. Stine it basically acted like a kiddie version of Tales from the Crypt having a new original story every episode.
In this episode two siblings played by Zach Lipovsky and Meredith Henderson find a secret passageway in their basement while looking for their birthday present. When they go through the passageway they end up running into a vampire who begins chasing them.
Along the way they run into a girl named Gwendalyn (Krista Dufresne) who assists them with running from the vampire. This was all a trick as it's later revealed the Gwendalyn herself was a vampire.
Eventually the two syblings escape just to find out in a twist ending that the vampire was their grandfather and that they come from a family of vampires.
On top of that, now that they're officially teenagers they too are now vampires.