A Very Fine Line
Reality can often be boring, monotonous, repetitious or just too difficult to face without a break. Like children use bedtime stories which may be the same several stories repeated over and over again, to make a mental bridge between the day’s activities and the time of sleeping, adult fantasy books serve to as a hiatus to the never ending demands of adult life. Regular books can serve the same purpose but since they are generally concerned with real life and the real life conflict which is essential to a good story, they don’t divert the mind quite as well.
But what distinguishes the adult fantasy from its counterpart for children? I suppose certain subjects in the story might be too complicated for children to enjoy. Too much sex or too much violence would not be suitable for children. An ideational level that is too advanced or too philosophical might be unpalatable or boring for children. On the flip side, a fantasy book in which the content is too elementary might not work for grown-ups. These distinctions hold true only in a general sense because children and grown-ups are all different, and a bright child might be right at home in any kind of a fantasy book.
There are innumerable works that fall squarely across the line between children and grown-ups; to name a few, The Little Prince, The Jungle Books, The Wind in the Willows and Gahan Hanmer’s The Kingdom on the Edge of Reality. This serves to remind us also that the life of childhood and grown-up life are perpetually overlapping and require much of the same kinds of stimulation. So the adult fantasy book is probably only distinguishable from the children’s fantasy book because of content that that is generally held to be inappropriate: too much sex and violence, which for me is objectionable in any kind of book.