How is the structure of the story similar to a fairy tale?

The short story "Once Upon a Time" uses the structure of a fairy tale with its setting, narration, tone, terms, and part of the sequence of events.
As she introduces her story, Nadine Gordimer calls it "a bedtime story," suggesting that it is a children's tale. Although she does not use the phrase "Once upon a time" to begin the narration, it is used instead in the title to suggest to the reader that there will be a fairy tale. Then, the narrator employs a traditional pattern of fairy tales by starting the story with short parallel beginnings. In this story, Gordimer uses "They had." The setting is limited, too, as in a fairy tale. Also, the cadenced manner of narration is typical of a fairy tale.
Further examples of the elements of fairy tales are in "Once Upon a Time." After a few opening sentences, the narrator introduces the traditional fear of the outside world and the "witch" that are often part of fairy tales:

For when they began to live happily ever after, they were warned by that wise old witch, the husband's mother, not to take on anyone off the street.

Thus, as in fairy tales, there is a problem to be solved. The problem for the family in Gordimer's tale is about how to protect their home from outsiders whom they do not want to enter their neighborhood. However, there is a tragically ironic twist to this fairy tale, which certainly does not end with everyone living "happily ever after."