Fairytales have stock characters - the witch, the fairy godmother and so on - but you then develop your witch, your fairy godmother and flesh them out. What do your characters make of the rules themselves? My rebellious fairy godmother, Eileen, hates them and her name change to a drab sounding Earth one is in itself an act of protest against what she sees as magical power abuses.
Fairytales can get great messages across without preaching. They can be funny, sad, or both though the ending has to be decisive one way or the other. Fairytales can explore issues or just be straight entertainment. Fairytales can be and usually are aimed at adults as well as children. Adults will have picked up the themes behind The Ugly Duckling and The Little Mermaid to name just two examples and be able to identify with them.