Three short lines are all Soju needs to stage a small catastrophe. A child who asks questions is shut down by the very people who should be answering them. The central idea is that silencing curiosity is a quiet kind of damage, and it is all the harder to notice because it can look so ordinary.
The title comes first and does a lot of work. «Shut Up» is printed in quotation marks, so it reads as speech, and the speakers are the parents we have not yet met. We hear the command before we learn who it was aimed at. The poem then reads like evidence laid out after a verdict. There is also an irony in who gets to speak. The child has no words anywhere in the poem. The only voice we hear is the adults', and it says just two syllables.
The construction is spare in a way that matches the subject. There is no rhyme, and "child" and "mouth" do not chime, so the poem offers none of the closure that rhyme can give. The lines also shrink as they go: seven syllables, then four, then three. The first line, "He was a curious child," moves easily, with a gentle rise and fall, like the open, wandering way a curious mind moves. The second, "Yet his parents," is cut short and hangs at the line break. The third, "Zipped his mouth," begins on a hard stressed syllable and is over almost at once. The poem narrows as it goes, like a zip being pulled closed.
The word choices repay a slow look. "Curious" is the only adjective, and it is a warm one. Nothing in the first line suggests a problem child. The verb "was" is worth noticing too. Because it is past tense, the curiosity feels like something that belongs to an earlier version of the boy. We are told what he used to be, and the poem lets us wonder what he is now. Then comes "Yet," the hinge of the poem. A curious child ought to be met with answers, patience, maybe delight, and "yet" announces that the expected response has not arrived. The phrase "his parents" sharpens the turn, because the possessive stresses closeness. These are the people most responsible for him, which makes the next word land harder.
That word is "Zipped." As a metaphor it is both clever and chilling. A zip is quick and mechanical, and it makes a small buzzing sound as it closes. It is something you do to a coat, a bag or a tent flap without a second thought. By choosing it, the poem suggests that the parents act without anger or even effort, just tidily and automatically. Nobody shouts and nobody hits. The violence is all in the casualness, and that is what makes it unsettling. The metaphor also turns the boy into an object, something with an opening that can be fastened when it becomes inconvenient. A zip can be undone, and I think that detail is worth pondering, but the poem does not say whether this one ever is.
The final noun matters as well. The poem could have said the parents stopped his questions or crushed his curiosity, but it says "mouth." The poem begins with a quality of mind and ends with a part of the body. For a child, curiosity lives in the mouth, in the endless "why?" and "what's that?", so closing the mouth closes the child's way of reaching into the world.
What makes the poem significant is how much it leaves out. We are not told what the child asked, why the parents reacted this way, or what happened afterwards. Perhaps they were tired, embarrassed or afraid of the questions, and the poem does not say. Because of this gap, readers have to supply their own context, and most will find a memory of being told to be quiet, or of saying it to someone else. The poem also behaves like the thing it describes. It stops quickly, before anything more can be said, and it gives the child no reply. In the silence after "mouth," the reader is left holding the questions the boy was not allowed to ask.