The poem begins by describing a woman known simply as "Aunt Sue," who is hugging a "child" and telling him "stories." Aunt Sue may be the child's aunt, the speaker's, or both (if the child is interpreted as the speaker's younger self). The language of the opening lines is plain and full of repetition:
Aunt Sue has a head full of stories.
Aunt Sue has a whole heart full of stories.
Notice the use of anaphora (the repetition of "Aunt Sue has a"), epistrophe (the repetition of "full of stories"), and more general parallelism (these sentences are structured in the exact same way). All of this repetition creates instant rhythm and musicality, carrying readers along as if they, too, are privy to "Aunt Sue's Stories."
At the same time, the parallelism draws attention to the few words that aren't repeated: "head" and "whole heart." In this way, the poem juxtaposes having a "head full of stories" and a "whole heart full" of them, suggesting that the two are subtly different. Aunt Sue isn't just someone who likes to dream up tall tales or recite interesting anecdotes; rather, she's someone who carries so many stories inside of her that she's practically overflowing with them. That they come from the "heart" suggests they are deeply significant to her; they are either personal memories or the memories of those who came before her and likewise passed them down.
Repetition isn't the only effect that creates rhythm and emphasis here. This first stanza is also full of alliteration and sibilance. The /h/ sounds in "head" and "whole heart," for example, further stress the contrast between stories that come from the mind and those that come from deep inside. Aunt Sue seems to have both, but the stronger alliteration of "whole heart" places greater emphasis on the second kind.
Meanwhile, sibilance adds to the poem's gentle tone:
Summer nights on the front porch
Aunt Sue cuddles a brown-faced child to her bosom
And tells him stories.
The soft /s/ and /z/ sounds mirror the softness of Aunt Sue's embrace as she "cuddles" this "child to her bosom." They also suggest the tenderness with which she shares her stories.
The poem is written in free verse, so it doesn't use a meter or rhyme scheme. Instead, its repetition and alliteration create more natural, conversational rhythms. In this way, its sound matches its subject: intimate storytelling. These free-flowing, yet rhythmic lines evoke Aunt Sue's kind of narration: sitting on "front porch[es]" during the "Summer," holding a relative close, and speaking from the "heart."