Every singer has his or her own vocal range. When they try to go outside that range, they will struggle to stay on point. In writing, every writer also has a writing range in terms of genres or creativity. However, children writers have the widest range of stories they can write. They may not be as logical or sophisticated in thought as adults but they are surely more creative, more daring and more fun than us. With these advantages, they can write stories that only children can.
As such, they should write the most crazy, absurd novels and the most imaginative fiction they can possibly conjure up. Restricting them or telling them that “this doesn’t make sense” or “that’s not physically possible” is like putting weights on an eagle. Instead, they should be allowed and encouraged to go as extreme (of course, appropriately so) as they wish with their stories because there is no right or wrong in story writing. This will develop a child to be possibility focused instead of problem centered. Children will learn to be creative and explorative in problem solving, ready to take initiative when challenged.
Not everyone may find enjoyment in reading very imaginative writing, but just like abstract art, beauty is in the eyes of the beholder and children should not be afraid that their fantasies receive negative feedback.