The Witches by Roald Dahl,

This is not a fairy-tale. This is about real witches. Real witches don't ride around on broomsticks. They don't even wear black cloaks and hats. They are vile, cunning, detestable creatures who disguise themselves as nice, ordinary ladies. So how can you tell when you're face to face with one? Well, if you don't know yet you'd better find out quickly-because there's nothing a witch loathes quite as much as children and she'll wield all kinds of terrifying powers to get rid of them