What makes a great work of children's literature great?

A friend and I are planning to collaborate on writing some children’s fiction. We have been discussing the elements of good children’s literature. I think originality, characterization and plot are key. We are talking about whether there needs to be some didactic element as well or whether that is more of an outdated idea. Obviously, one needs to decide what age one is writing for and whether the book will be a picture or chapter book. Would like to hear some Jelly opinions on what makes great children’s books for you, with example if you have them. I have my own personal favorites, of course, but would like some collective wisdom. Thanks.