"The Celery Stalks at Midnight" by James Howe (Bunnicula and Friends, Book 3)

Bunnicula is missing! Chester is convinced all the world's vegetables are in danger of being drained of their life juices and turned into zombies. Soon, he has Harold and Howie running around sticking toothpicks through hearts of lettuce and any other veggie in sight. Of course, Chester has been known to be wrong before...but you can never be too careful when there's a vampire bunny at large!