The Magic Finger by Roald Dahl.
An eight-year-old girl (unnamed narrator) has a Magic Finger — when she gets very angry, it fires a powerful spell at whoever made her angry. When her neighbours the Gregg family go duck hunting, the girl is so upset that she points her Magic Finger at them. The Gregg family wake up to find they have turned into ducks — small, with wings instead of arms — while four ducks have moved into their house and are living as humans. Mr Gregg has to provide for his family by building a nest in a tree and catching fish in his beak. By morning he has decided never to hunt again. The Magic Finger reverses the spell and the Greggs return to being human — but they never hunt again. They even invite ducks to come and live on their pond.