Very first: The Song of Wandering Aengus, by William Butler Yeats. I read this when I was six or so. I found it as an illustrated children's book in children's section of the public library of the very small rural town. Someone decided this very adult poem, about an old man who wasted his life chasing an unattainable magic dream, was a good children's story. It introduced me to the idea that poems and stories could express sadness and failure and other negative feelings, not just the happy silly stuff of the other age-appropriate things I read.