The speaker is talking to a kiddo named Margaret, who is crying her little eyes out over something or other. The speaker decides that she's crying because all the leaves in the forest of Goldengrove have died and fallen off the trees. (What, don't you cry every year when the leaves fall off the trees?) The speaker tells the child that as she gets older, she might not notice or care as much, but he also says that crying over the fallen leaves means something else: it shows that Margaret is starting to think about mortality and, yes, her own eventual death. That's right! This is a poem about death, addressed to a young child.