Walt Whitman did not write a poem titled "Miracles." It is likely you are thinking of one of his other poems, perhaps "Song of Myself" which features the famous line: "A child said What is the grass? fetching it to me with full hands; / How could I answer the child? I do not know what it is any more than he."
Could you provide more context or details about the poem you're thinking of? I'd be happy to help you find it.