Children have liberties too. Thus, I do believe the government does play a role in helping children receive the health care they deserve. A lot of what these super-religious parents are doing is called child-abuse, and they should be tried for that.
And let's not beat around the bush here. Religious freedom is one thing, magic is another.
There is no such thing as magic which could magically make sickness go away. And if you insist there is, without proof or explanation, then you defy the will of the god who has not intervened in humanity for thousands of years.
If you honestly believe you can pray away the worst of illnesses, you are a horrible parent who places your selfish own fantasy world above that of your own child.
Like I said: The child has liberties too. Just like it's wrong to abort a fetus, isn't it wrong to kill a child because one would rather believe that which is both scientifically, and religiously impossible?