You're first question is a false dichotomy (The answer, by the way, is "No, i don't"). When the interests of the child (as in the cancer case) is grave, then the parents should not have say-so in medical decisions when they make decisions contrary to the interests of the child, as determined by doctors. This, in essence, erases anything that can coherently be called a "right".
What "first" question? I only asked one rhetorical question.
So you would take the decision making process away from the parents and give it to doctors? (Another rhetorical question. Just one.) Yes, putting the decision in the hands of doctors does "erase" the parents' "right" to make medical decisions on their kids' behalf. Fortunately, that's not the way it works in the real world.
Doctors don't want to make those decisions anyway.