Ooh... took me a while for the implications to sink in. Just a little bit unpleasant, isn't it? and so true to the traditional character of 'fairy folk'... they are cruel in their treatment of humans. Very subtle and fine.
Editorially: One has proof of, not for, I think that's what you wrote... I should have copied it. and don't forget to put a comma before the person's name in speech, thus. "You'll be a good boy, Robin?".