I wouldn't say it's a claim. It is the actual story of it and originating from Germany under the titled of Aschenputtel by Jacob and Grimm. There's a page dedicated for folkstories like this from University of Pittsburg here and it's a work translated by Professor D. L. Ashliman who is known for his work on this subject https://sites.pitt.edu/~dash/grimm021.html. The actual tale of many so-called " Children's story" are actually pretty disturbing compared to the one we are familiar about. I actually found out about this during my mythology and folklore class where we examined stories like Cinderella and its different version across the world. If anyone interested, there's even a hanbook to study these by Ashliman too, it's called Folk and Fairy Tales: A Handbook.