Is the mother required to fast or offer any other expiation following the death of her child who choked on a piece of cheese, and is that considered negligence on her part?

There is no sin upon the mother, nor is there any blood money or expiation due from her, because eating cheese by itself does not originally cause death. The doctors' report clarifies that the cause of death was something attached to the cheese. As long as the mother was unaware of its presence, she did not commit any negligence or cause his death.