"In the Park" uses alliteration throughout all three stanzas. The effect is subtle, in keeping with the poem's conversational tone. Sometimes the moments of alliteration are quite space out as well—meaning they won't perhaps register as true alliteration, but do create a clear echo throughout the poem.
The first stanza, for instances, relies on the repetition of the /p/ sound in "park," "pattern," and "passed" to knit together the opening scene. These words aren't right next to one another, but still ring out clearly to the reader's ear. Combined with the many /t/ and /d/ sounds (which appear as both alliteration and consonance), the opening stanza feels rather spiky and percussive, reflecting the woman's discomfort and bitterness at her situation:
She sits in the park. Her clothes are out of date.
Two children whine and bicker, tug her skirt.
A third draws aimless patterns in the dirt
Someone she loved once passed by – too late
The shared /l/ of "loved" and "late," meanwhile, suggest a subtle connection between these words—that the time for the woman to feel "love" has passed her by.
In the second stanza, alliteration similarly binds together "great," "grace," and "God," the hard, guttural /g/ sound adding emphasis to the man's relief at not being stuck in the woman's situation.
Perhaps most importantly, the third stanza's alliteration relies on repetition of the /s/ sound in words like "stand," "so sweet," "smile," and "sits staring." This sibilance, or hissing created by the many /s/ sounds, is reminiscent of the sound of the wind, and also suggests whispers. It foreshadows the final line of the poem, in which the woman confesses to the wind (and perhaps, as befits such a dark truth, only in a whisper): that her children have consumed her life.