Who has seen the wind?
Neither I nor you.
We are not sure whether or not the speaker is addressing a younger person, but since this is a nursery rhyme, it can probably be assumed that "you" is a child. Regardless, in these first two lines, Rossetti establishes a question and immediately answers that question with a definitive statement—no one has seen the wind, not me, not you. If indeed she is speaking to a young child, then she is also explaining the nature of things that we cannot see, but know are there.
Interestingly, one should note the second line's inverted syntax of "neither I nor you." Although this construction serves to fit the ABCB rhyme scheme where "you" rhymes with "through", it also draws attention to the speaker and allows Rossetti to mirror this statement, albeit with correct grammar in the second stanza, which serves as an effective way to introduce a new B rhyme while maintaining the same sense as the first stanza.
Who has seen the wind?
Neither you nor I.
When Rossetti repeats these lines in stanza 2, she establishes a refrain, and since the poem is only 8 lines long, this refrain dominates more than half of the text. This simplicity makes the poem easy to remember, and even easier to speak/or sing along with. Children will be taken in by the simple meter, the obvious rhymes, and the questioning refrain. In this way "Who has seen the wind?" operates in a primarily didactic mode.
However, as mentioned above, Rossetti's subtle play with the syntax of "neither I nor you" and "neither you nor I" in lines 2 and 5 respectively, allows for a richer analysis of the poem. Looking past the rhyme scheme, how does reversing the order of the subjects, "you" and "I," change the meaning of the poem? Certainly, the syntactic shift also causes a shift in emphasis. "Neither you nor I" is less assertive than the former, and this softening in tone allows Rossetti to finish the poem in a less aggressive manner, simultaneously mirroring the wind "passing by."
But when the trees bow down their heads,
The wind is passing by.
This is one of the few examples of literary devices in the rhyme; the poet tells of trees that "bow down their heads", which both personifies and anthropomorphosizes the trees, giving them the ability to decide to bow, and also the physical feature of heads, rather than referring to the tops of the trees which would be more common.
It is also the way in which the poet explains that just because we cannot see something in itself, we can still see evidence of its existence. We cannot see the wind itself, but we know it's there because we can see the trees bowing in the breeze.
The trees also seem very reverent towards the wind. This is an element of the poem that seems to imply a greater meaning than that of a charming rhyme about nature; in explaining the nature of things that we cannot see but must take on faith by observing their effects on the world around us, the pious Rossetti could also be laying the groundwork for explaining religious belief and faith to a young listener.
