Technically, that would be serial killing instead of mass murder. Mass murderers usually know their victims.
The mother knows her child, there is no question about that.
Oh, there are technical differences, to be sure.
A mother killing her own child in the more heinous crime, here, though, and the numbers are more massive than anything in history, at least comparable.
Anyway, the murderer here knows the victim intimately. In fact, the victim’s cells are left in the mother/ murderer for life.