Possible Clues:

• Fairytale opening
• So the story starts with 15 across
• Introduction to children's literature?
• Long ago, I started any number of stories
• That's never at the end of the tail, by the sound of it
• That's never the tail of the tale
• Familiar initial words, but continue a poem differently
• Continue a poem translated years ago
• Cliched start in a poem -- continue working
• Traditional start of a story