"My Parents Kept Me From Children Who Were Rough" deals with class differences. The adult poet looks back at how it felt to be a child whose middle-class parents warned him to stay away from the "rough" working-class boys.
The poem's narrator is ambivalent. Like his parents, he is afraid of the rough boys, but he also feels a mixture of attraction, jealousy, and shame.
The poem begins, "My parents kept me from children who were rough." It would have been more accurate to say that his parents *tried* to keep him from children who were rough, because his parents weren't fully successful in keeping their son and the rough children apart.
The rough children follow the narrator on the road, imitating his lisp. They pin him down - "their knees tight on [his] arms" - or at least he feared that they would. There is a gap between his parents intentions and the reality of his life.
The narrator envies the freedom of the rough boys, the way they can run in the street, climb cliffs, and strip by the country streams. The narrator must have been expected to act with middle-class propriety, walking demurely down the street, never going outside wearing torn clothing.
To the narrator, the rough children are wild. He compares them to tigers and dogs. Like animals, the children were free from having to abide by suffocating middle-class conventions, and the narrator is jealous.
The tone of the poem shifts in the last two lines: "While I looked the other way, pretending to smile. / I longed to forgive them, but they never smiled."
The narrator only pretends to smile. Conventional polite middle-class behavior often requires people to put on a phony smile. That may smooth over some social interactions, but it also can create distance. A genuine smile brings people closer together. It is infectious. We instinctively respond to a genuine smile with one of our own. A real smile can bridge gaps between people, creating communication between people who speak different languages - or who come from different classes.
The rough boys, though, don't respond to the narrator's phony smile. The narrator is disappointed. But why did he "long to forgive them" in the first place?
At first glance, the line about forgiveness seems condescending - who is he to offer forgiveness to them? But there are two things he might have wanted to forgive. The first is the way the rough boys treated him personally, making fun of his lisp and pinning him down. The second is for their side in the class struggle, their "bark[ing]" at the narrator's world.
Unless the narrator can offer more than a phony smile, though, his offer of forgiveness will not be accepted. Perhaps that is what Spender, as an adult poet, now realizes as he looks back at an earlier time.