On orphans in children’s books

What is it about orphans in books? They are tragic, with backgrounds mysterious, bruised, like Jane Eyre. They are vulnerable and burdened, like Oliver; or have learned to be trickier than the trickiest, like the Artful Dodger. They are steely, sad, often hungry with large eyes. They’re tragically young and terrifically youthful. They are tantalisingly free.