I keep thinking of this story from like 50 years ago... I had to go look it up. It relates to your ongoing discussion about Conix's "sister".
A Summary and Analysis of Shirley Jackson’s ‘Charles’
‘Charles’ is a short story by the American writer Shirley Jackson (1916-65), first published in the women’s magazine Mademoiselle in 1948 and included in her 1949 collection, The Lottery and Other Stories. The story is about a young boy who, upon starting kindergarten, picks up bad habits which he attributes to the presence of Charles, a boy in his class.
‘Charles’: plot summary
The story is narrated by a mother, who observes that her son, Laurie, began to grow up when he started kindergarten. He wore different clothes and forgot to turn and wave to her when he got to the end of the street.
When Laurie is rude at the dinner table after his first day at school, the narrator calls him out on it, and he says that a boy at school, named Charles, was rude to the teacher and was spanked as punishment. The next day, he tells his parents at lunch that Charles has misbehaved and struck the teacher. This pattern of bad behaviour continues throughout the week, until the narrator asks her husband whether this Charles is proving to be a bad influence on their son. But they convince themselves it will be all right.
The following week, Laurie comes home and reports that Charles has misbehaved again, receiving detention: everyone in the class stayed behind with him. Then, Charles kicks a friend of the teacher who comes into class to show the children how to exercise. The family come to use the name ‘Charles’ to refer to anyone in the family who has done something naughty.
But over the next few weeks, Charles appears to reform his behaviour and becomes the teacher’s helper. But then he relapses, and Laurie comes home and tells his parents that Charles got into trouble for persuading a girl in the class to say a rude word to the teacher. The narrator resolves to find Charles’s mother at the parent-teacher meeting and find out what is going on with her son.
But at the meeting, she is unable to identify any woman who might be Charles’s mother, and when she gets talking to Laurie’s kindergarten teacher, she learns that there is no child named Charles in the kindergarten and that the behaviour Laurie had ascribed to ‘Charles’ was really his own.