If the parents are going against the child's best interests, then the choice should be made by medical professionals. They have to go through years of training, they have better knowledge to make a decision on a child's health. Not attending to a child's health care is a form of neglect and has lead to the avoidable deaths of dozens of children over the last 10 years alone. Parents do not and should not have the right to deny a child's medical care, regardless of their beliefs because it's not their life that they are risking by denying care, it's a vulnerable child's.
Until a person is able to give informed consent about personal health matters, the decisions made should be trusted to the medical professionals rather than a parent. Medical professionals have been trained, educated, and licensed for medical matters while the average parent is not. They have put in the time and money needed to gain the knowledge necessary to practice medicine. The networks and resources available to a medical professional are far greater than to the average parent. Parents are going to be more emotional about the decision to be made and a medical professional can make decisions with minimal interference from emotions.
I know parents want to be protective of their kids and always think they know what is best for them, but they really should listen to medical professionals when it comes to diagnostics and plans to treat the children. Doctors will fail somtimes, but not as often as parents do when it comes to medical issues.
I believe a parent knows their children and can diagnose a problem better than a medical professional if given the right information. I think a parent should have the right to get a second opinion for their child if they feel its in the child's best intrest and also be allowed to deny treatment if they are not comfortable with the decision, the doctor or the hospital they are given.
Unless some laws are being broken, the parents of a child should have the final say in regards to what should be done about any health issues their kid is dealing with. If a child's parents do not agree with a medical procedure that a doctor want to implement on a their kid, then the parents should not have to agree to it.
Parents should give heavy thought about what the medical professionals are telling them. If they sound like they are being genuine, then the parents should do what their doctors tell them. If they sound like they are just giving the parents the run around to make money, then the parents should look for other options.