A shelf for the question your child may not have asked you out loud. Not where they sleep on Tuesdays, not whose house the rabbit lives at. The other one. Did I do this? Could I undo it if I were good enough? Pick the one that matches your child's age and what they seem to be circling this week. It's Not Your Fault, KoKo Bear is a good place to start if you don't know where to go in, because it says the answer in the title and then keeps saying it, which is roughly how often it needs saying.
What holds it together is one mechanism, and if you've never had it named you will recognize your own child in about four seconds. A small child works out cause and effect by watching their own behavior. So when a family comes apart, they go looking for what they did. They find the last bad thing before everything changed, and they connect the two, and then they say nothing, because if it was theirs then saying it out loud makes it real. Was It the Chocolate Pudding? is built entirely on this and it's the most useful thing here. A boy is certain the divorce happened because he and his brother smeared pudding up the wall. It's absurd enough that your child can see it isn't true and close enough to their own arithmetic that they recognize the shape. Watching a boy be wrong about it is much easier than being told you're wrong about it. KoKo Bear comes at the same target from the front, saying it in the title and then repeating it across the book, which is the right instinct, because nobody believes this the first time. Then there are the ones that give a child somewhere to put the feeling rather than an argument against it: Two Homes counts what's still there instead of explaining what's gone, Fred Stays with Me! hands the whole business to a dog, and The Invisible String answers the version of the question that's really about missing someone. Dinosaurs Divorce is the outlier and admits it, a manual with headings, for a child who wants it all laid out. And the two novels are a different act altogether. Sunny Side Up is not about a divorce at all, which you need to know before you buy it. Bigger Than a Bread Box gives a girl real working magic and then makes her live with the fact that it can't reach the one thing she wants.