does two things right away: It sets up a world and then it subverts its own rules even as it follows them. It works like a sonata of sorts, but, like a good version of the form, it does not follow a wholly predictable structure. Many children’s books do, particularly for this age, as kids love repetition and the books supply it. They often end as we expect, with a circling back to the start, and a fun twist. This is satisfying but it can be forgettable. Kids — people — also love depth and surprise, and “Goodnight Moon” offers both. Here’s what I think it does that is so radical and illuminating for writers of all kinds, poets and fiction writers and more.