Even based on religious rights I do not view that parents should be allowed to without medical treatment to save their child's life. Their child should have a choice to based on their own personal beliefs. Even if the child is extremely young, as in six or older, they should be allowed to choose whether they want a chance to live, or late things take their course. It is not right for parents to purposeful hide information that may benefit the child and allow the child to live a longer life if that is what the child decides.
Children are not old enough to make decisions by themselves to withhold medical treatment due to religious reasons, and Parents shouldn't be allowed to make their children withhold medical treatment either. If a parent forces a child not to receive medical treatment then that an equivalent to child abuse in my opinion as a person is entitled to their human rights of treatment. I'm talking about things as life threatening as needing a blood transfusion. Things like that can mean the difference between life and death