But the big difference here is between someone making such a decision on their own behalf, and on behalf of someone for whom they are the guardian. Did the child want to die rather than go to a hospital? Those parents can fight their own cancers with laetrile if they want, for all I care--but making the decision to pray only for an unconscious 11 year old child for whom they were responsible is different. If your religious beliefs allow you to kill your own children through inattention (or starvation or exposure on a mountainside or whatever), then I've got a problem with that. That's no longer a self-determination issue.
Also, as noted above, had it worked they would have faced no problems--indeed, who would have known? They made a bad choice--evidence that they did use a reasonable standard of care w.r.t. the child.
When God starts healing broken arms at the same rate that orthopedists do, or internal bleeding as well as a general surgeon, then we can reconsider the matter. Until then, it's really about the concept of an age of majority, and the care due a minor who is legally unable to obtain her own health insurance and too young to make informed decisions.
But it does open a slippery slope. What if some government official decides that I cna't have my boys circumsised at 8 days because they can't give consent? Or that I should use a specific treatment for a cold?
While I would have rushed my kid to the hospital, it is a hard thing to judge.