I can understand your point but I still believe that the rights of a parent, their beliefs and values should be respected. I imagine in their eyes that if a child was given a transfusion they would be condemned, if then they also went on to develop CJD they'd die anyway and would be condemned to hell, so in their eyes they'd be saving their children from being damned.
I'm not saying that I agree with their choice, I and my children would have blood transfusions if it was necessary, but I do think that it's wrong for their rights to be taken away because the medical world and people outside their religion don't agree with them. You argue that the child doesn't get a say, well what if they wouldn't want it either? Why should a blood transfusion be imposed on them because a stranger says it should?