The Little Girl and the Wolf by James Thurber

One afternoon a big wolf waited in a dark forest for a little girl to come along carrying a basket of food to her grandmother. Finally a little girl did come along and she was carrying a basket of food. "Are you carrying that basket to your grandmother?" asked the wolf. The little girl said yes, she was. So the wolf asked her where her grandmother lived and the little girl told him and he disappeared into the wood. 

When the little girl opened the door of her grandmother's house she saw that there was somebody in bed with a nightcap and nightgown on. She had approached no nearer than twenty-five feet from the bed when she saw that it was not her grandmother but the wolf, for even in a nightcap a wolf does not look any more like your grandmother than the Metro-Goldwyn lion looks like Calvin Coolidge. So the little girl took an automatic out of her basket and shot the wolf dead. 

(Moral: It is not so easy to fool little girls nowadays as it used to be.)