The title of the poem, "Arms and the Boy," has two parts—the arms… and the boy. Before you say duh!, hear us out. Including both those things in the title helps set us up for the poem's double focus: the boy soldier and the weapons of warfare that he must learn to use.
The separation of the arms from the boy suggests how alien the use of weapons of warfare was for young, unsuspecting soldiers during World War I, but it also describes one of the poem's major themes: that young men aren't naturally violent and bloodthirsty. Rather it's the circumstances in which they find themselves, and the weapons they're handed that make them kill (or be killed).
"Arms and the Boy" doesn't just tell us what the poem's about. It's also an allusion to a play by the Irish playwright George Bernard Shaw called Arms and the Man (first performed 1894, published in 1898). Shaw's play takes place during a war, but it's a comedy and ends happily. So that's new.
Or is it an allusion to Virgil's Aeneid, which starts off, "I sing of arms and man" (arma virumque cano)? The Aeneid is an ancient Roman epic poem that glorifies military heroism and the discovery and conquest of a new land (present day Italy).
Can it be an allusion to both? Absolutely. Owen takes two famous literary examples and, in just 12 lines, shows how hollow and wrong their ideas about warfare are. There's no glory in "Arms and the Boy," and by switching it from "Man" to "Boy," he shows us that these youngsters are dying in spades, and though we may call them men, they aren't by any stretch. They're boys, and they shouldn't be fighting.