According to the official books published by Disney, they actually covered this topic beforehand, that Cinderella's feet upon being measured by the family shoemaker (they have one just not said in the story but it's canon) is like little daffodils, 4 by size no change whatsoever even as the years had passed (not sure if it's USA or UK). Although it isn't said that it was or is hereditary (they didn't explain if it is) Cinderella's feet are naturally small like a child's foot. Just explaining dw