Your child closed the last Narnia book and wants another door. Here are six. Any one of these will land for a child who loved Narnia, so pick by your child's age and by how much weight they can carry, and hand it over. One of these is pure sunshine. One of them will make them cry about a horse.
Narnia does three things at once, and no single book does all three, so this shelf splits them up. There is the door, the idea that a wardrobe in your own house could open onto somewhere else. There is the war, a real one, where the choices cost something. And there is the moral weight, the sense that the story is about more than what happens in it. Half Magic is the door with the sun on it. The Phantom Tollbooth is the door plus a very funny brain. The Book of Three is the war, in a formal, Welsh-legend voice that sounds a lot like Lewis. A Wrinkle in Time and On the Edge of the Dark Sea of Darkness both carry the weight. And The Neverending Story takes the door and walks all the way through it, then asks what it costs to stay. Worth saying plainly, because families come to Narnia from opposite directions and both are here on purpose: some parents love it for the Christian allegory and some love it despite it. On this shelf, A Wrinkle in Time quotes scripture and names Jesus among the lights fighting the dark. The Wingfeather book is by a Christian songwriter on a Christian imprint, its characters pray, and it assumes a Maker, though book one has no sermon in it. The Book of Three is Welsh myth with no religion at all. The Neverending Story has no religious frame by design. Half Magic and The Phantom Tollbooth have nothing of the sort. That is a fact about each book, not a mark for or against it, and you know which way you are choosing.