In order to fully appreciate the symbolism in "Once Upon a Time," it is important to place this work in its historical context. Nadine Gordimer grew up in South Africa during the country's apartheid era. The daughter of Jewish immigrants, Gordimer was strongly opposed to the racism around her and made this the focus of much of her writing.
In "Once Upon a Time," Gordimer rejects the notion of an idyllic bedtime story and instead tells a story of her own experience. This story is the story of South Africa, where the lines of racism were drawn and white supremacy was celebrated.
The phrase "happily ever after" is repeated numerous times throughout the story, symbolizing the superficial sense of happiness that the family constructs their lives around. Of course, the phrase is juxtaposed with other images, such as windows that are eventually covered with bars, and later with the coils that are installed around the family's home. This repetitive and ironic symbolism demonstrates the façade of happiness which the couple constructs; they are determined to maintain their lifestyle even if they inflict death on people who dare to cross the lines they create.
The coil of wire which the couple places around their home symbolizes apartheid itself. The wire is described in vividly destructive terms:
It consisted of a continuous coil of stiff and shining metal serrated into jagged blades, so that there would be no way of climbing over it and no way through its tunnel without getting entangled in its fangs. There would be no way out, only a struggle getting bloodier and bloodier, a deeper and sharper hooking and tearing of flesh.
Like the wire, apartheid functions to destroy lives, tearing people and bodies apart with its hooks and snares. Apartheid is violent and destructive, and it is dangerous on both sides of the "fence." While the couple believe themselves safely hidden away on the "proper" side of the fence, they fail to realize that their son is at risk because of the fence they have constructed.
The boy is symbolic of innocence. He enjoys the world around him, playing games with the increasingly deadly fortifications. He has no sense of the danger he is supposed to feel. Instead, he runs ahead of his parents on their walks and enjoys creative games with his friends. The boy is full of imagination and energy, and he doesn't exist in the same world of fear which dominates his parents' efforts.
At Christmas, the boy is given a book of fairy tales. This book is symbolic of the couple's disillusionment with the world around them. They are living a fairy tale every day, determined to believe that they can both be a part of and separate from the suffering around them. They refuse to leave the community where they have to first install a gate, and then bars, and then, later, a deadly wire to keep out people whom they have deemed unworthy. They also believe that they can live "happily ever after" in the midst of constant fear and surveillance. The book of fairy tales is the young son's impetus for choosing to scale his parents' deadly divide, and he dies because of those efforts.