Two children play at the shore on a grey day, delighted by the white-capped waves. They don't care that it's Monday, and they don't notice the "grim anguish" of their parents. The poem sets that innocent joy against a quieter, sadder scene: far out, a three-sailed ship sits on the horizon and then slips silently out of sight.
The final stanza turns to questions. Someone stands "before the mast," but the speaker can't tell whether it is a real man or only his shadow. The image suggests a person who is absent, perhaps lost or gone, though the poem never says exactly what has happened. The last lines imagine a child's full heart, holding his hand, steering by a "forgotten star" to bring him home.
The mood is wistful and hushed, mixing grief with tenderness. The speaker seems to find a fragile hope in the children's uncomplicated joy, even while the grey sea and the vanishing ship keep the loss in view.