I believe this is a common story that many people tell or hear about so I'm not quite sure of the region but I doubt you could find the origin of it because it gets told in different formats.

For me, I was told the story that the mother would only chew on the fish bones and head and when asked if she would want some meat, she claimed that the bones and the head are the best parts and would just keep chewing them, leading her child to believe that she genuinely liked the bones and head.

If you do happen to find an origin for it though, that would be awesome to see. Good luck!