Goosebumps Vampire Breath by R. L. Stine

Freddy and Cara are friends that find a hidden door in Freddy’s basement. They find a tunnel and decide to explore it. Freddy and Cara find a coffin with a bottle of Vampire’s Breath. They fight over the bottle. The bottle falls and opens. They travel back in time. An old Vampire named Count Nightwig appears in the coffin. The kids and the vampire travel forward in time. Freddy finds out Count Nightwig is his grandpa and that he is a vampire too.