Existing laws have gradually accounted for more well-known and established faiths, such as Pentecostalism, Christian Science and Jehovah's Witnesses.
But recent cases in the news have judges and child care advocates dealing with parents who claim adherence to lesser-known faiths, such as the Minnesota family following an Internet-based group's American Indian beliefs, and an independent church in the western state of Oregon that has been investigated in the past for the deaths of members' sick children.
Legal and religious scholars say it's becoming more difficult for courts to decide when to honor the religious beliefs of parents and when to order conventional medical treatment for extremely sick children.
The manslaughter trial of an Oregon couple who claim they were following their religious beliefs in the 2008 pneumonia death of their 1-year-old daughter began Monday. Carl and Raylene Worthington are members of Followers of Christ Church, which has been investigated for past child deaths.
In Tennessee, Jacqueline Crank and her minister Ariel Sherman face child neglect charges in the death of her 15-year-old daughter Jessica, who died in 2002 with a basketball-sized tumor on her shoulder. Prosecutors say based on Sherman's advice, the girl's mother relied on prayer instead of medicine.
Sherman has been accused of being a cult leader whose Universal Life Church is not a legitimate religion. He has denied such charges and says the church is Christian-based and embraces the Bible.
Believers in faith healing point to a Biblical verse in the Epistle of James, which describes how church elders should be called in to pray over the sick. There's no mention of doctors, and literalists interpret it to mean medical treatment should be eschewed over prayer.
Gregory P. Isaacs, an attorney for Crank, who is out on bond, argues that Tennessee's religious exemption law is untested and too vague.
"It really has a tremendous amount of problems," Isaacs said. "What is an organized religion and what is an ordained minister? What illnesses can you attempt to heal by faith? Those are the two pitfalls in the statute. That's not what's really clear."
Jim Dwyer, a William and Mary Law School professor who has written articles about and participated in litigation on the topic, said it is often more complicated for courts to discern cases with unaffiliated religions because judges and juries aren't as familiar with them and are skeptical of their legitimacy.
"The Supreme Court has adopted a very broad definition of religion," Dwyer said. "But ... you have to show sincere religious beliefs. Some judges might be skeptical of sincerity if it's something they've never heard of, if the person says, 'I don't belong to a certain church. I just have some beliefs that I saw on the Internet,' or 'In our own home, we've developed this set of beliefs."'
Dr. Ellen Wright Clayton, a pediatrician and co-director of the Center for Biomedical Ethics and Society at Vanderbilt University, says when treatment for an illness is very toxic and the prognosis is dire, courts tend to rule parents don't have to pursue medical treatment. If that's not the case, courts are likely to order the treatment.
"Until medicine became effective, there was no push to say we absolutely have to do medical treatment. There wasn't this notion of deference (to religion) until medicine began to work and to become institutionally powerful."
Besides the states that have religious exemption laws, five states — Hawaii, Maryland, Massachusetts, Nebraska and North Carolina — have repealed such laws.
Many of the exemption laws were enacted in the 1970s. Rita Swan, director of the Sioux City, Iowa-based advocacy group Children's Healthcare is a Legal Duty, which lobbies states to repeal such laws, said that since 1975, there have been at least 274 known cases of U.S. children who have died after medical care was withheld on religious grounds.
She says the majority of such cases are still associated with established denominations like Pentecostalism, though "the Internet has opened up some more possibilities than it did before" and there have been some cases involving unaffiliated denominations.
At least two recent high-profile cases involve parents whose beliefs were drawn from Internet-based religious groups.
Authorities in Minnesota convinced a judge to force 13-year-old Daniel Hauser into chemotherapy, prompting his mother Colleen to skip a court hearing and — with her son in tow — go on the run for nearly a week in May.
They headed to Southern California, where they considered a trip into Mexico for alternative cancer treatments, before eventually returning to the Hausers' home. The boy has since received chemotherapy treatments, which appear to be working.
The family prefers natural healing practices suggested by an Internet-based group called the Nemenhah Band, which says it follows American Indian beliefs.