Some people used to say that fantasy and fairy stories were just for children. Here are some thoughts by J.R.R. Tolkien about whether any branch of genuine art should be just for children:
The process of growing older is not necessarily allied to growing wickeder, though the two do often happen together. Children are meant to grow up, and not to become Peter Pans. Not to lose innocence and wonder, but to proceed on the appointed journey: that journey upon which it is certainly not better to travel hopefully than to arrive, though we must travel hopefully if we are to arrive. But it is one of the lessons of fairy-stories (if we can speak of the lessons of things that do not lecture) that on callow, lumpish, and selfish youth peril, sorrow, and the shadow of death can bestow dignity, and even sometimes wisdom.
Let us not divide the human race into Eloi and Morlocks: pretty children … with their fairy-tales (carefully pruned), and dark Morlocks tending their machines. If fairy-story as a kind is worth reading at all it is worthy to be written for and read by adults. They will, of course, put more in and get more out than children can.
Then, as a branch of genuine art, children may hope to get fairy-stories fit for them to read and yet within their measure; as they may hope to get suitable introductions to poetry, history, and the sciences. Though it may be better for them to read some things, especially fairy-stories, that are beyond their measure rather than short of it. Their books like their clothes should allow for growth, and their books at any rate should encourage it.
— J.R.R. Tolkien
Tree and Leaf, pages 44-45,
First American Edition, 1965 A.D.