They should've been sterilized and had their children taken away when the first one died. I blame the authorities for the death of that child as much as the loony parents.
People like this should have their children taken away and their parental rights suspended the moment they fall ill, in the interest of the child. They can have them back when they're recovered and teach them whatever nonsense they like, but they should not be permitted to allow their religion to murder their children for them.