[Kevin]

We don't allow parents to actively harm their children, even in the name of religious worship. There is no doubt in my mind that if instead of refusing to treat this cancer, the parents were savagely beating a healthy boy, the state would step in because such savage beatings could and probably would eventually lead to death -- even if the parents believed that those savage beatings were necessary for salvation.

How is this any different? This mother is, by her inaction, rather than action (what's the difference?) bringing about essentially the same result -- her child will die due to her inaction. This parent has a duty to do everything to protect her child. When she refuses to do her duty, the state needs to step in. This is how a civilized society deals with a failure in the parent-child relationship.