Comment by thaumasiotes

There's a good children's book about Eskimo undersea child-snatching monsters: https://www.annickpress.com/Books/A/A-Promise-Is-a-Promise

They don't use bags, though it's always possible that that's an adaptation of the original story. It seems more likely that there is cultural variation in traditional stories.

There is no need to make it impossible for a monster to target adults. You can just say that they target children.

https://en.wikipedia.org/wiki/Qallupilluit