The legal definition of insanity is a very narrow one. I seriously doubt that this couple fits that definition. I suspect that a charge of involuntary manslaughter could stick, but that's a tough call.

Remember, the parents may have freedom of religion, but that does not give them the right to cause the death of another, either through action or inaction, no matter now justified they may feel. This has been tested in courts many times, frequently involving Jehovah's Witnesses and blood transfusions or Christian Scientists and necessary surgeries. Generally the safety of the child, who has no say in the matter, is considered by the court to be paramount.