OREGON CITY, Ore. -- The manslaughter trial of an Oregon City couple who claim they were following their religious beliefs in the death of their 15-month-old daughter began Monday with a disagreement over how ill the child was.

Carl and Raylene Worthington belong to the Followers of Christ Church, which has been investigated in the past for child deaths. Church members shun doctors in favor of spiritual healing.

The Worthingtons' daughter, Ava, died March 2, 2008, of pneumonia that the state medical examiner ruled could have been easily cured with antibiotics.

Prosecutor Greg Horner said in his opening statement that the infant lost a months-long battle with pneumonia, accompanied by a cyst on her neck that put pressure on her esophagus.

Defense lawyer Mark Cogan said the child was playing and eating normally in the days before she died, and the couple didn't believe she needed medical care.

The couple have already lost a round of defense motions before trial in Clackamas County Circuit Court, including a claim they were targeted for prosecution because of their church.

Clackamas County Circuit Judge Steven Maurer told defense attorneys that it would be up to a jury to decide the value of photographs of their dead child.

The couple believes they shouldn't face trial on manslaughter charges in her death.

The couple also claim they were within their constitutional rights when they decided to pray for their 15-month old daughter rather than take her to a doctor to treat her pneumonia.

But legal experts believe that Carl and Raylene Worthington will likely have a difficult time arguing freedom of religion over the state's duty to protect children from harm.

The trial comes about a decade after the Oregon Legislature amended state law to restrict an exemption for faith healing and to bar arguments that religious beliefs prevent seeking medical help.

The revision in state law came in response to an investigation into a series of deaths of children whose parents belonged to the church and suffered from untreated illnesses that were curable.

A small church cemetery is lined with the graves of dozens of children -- suggesting an extraordinary increase over the average death rate for children in the United States, according to Dr. Seth Asser, a Boston pediatrician who has studied the practices of faith healing groups for years.

He said such deaths are far more common among fringe groups with small congregations that stand apart from mainstream churches.

The deaths also typically involve young children because "by the time kids are school age, there are others involved in their lives -- friends, neighbors, family, teachers that may be aware if there's a serious issue," Asser said.

The judge in the case, Clackamas County Circuit Judge Steven Mauer, said at a hearing in January that "I do not feel we are on unplowed legal ground" before he rejected a defense motion to dismiss the charges.

A number of legal experts agree the law is fairly well settled when it comes to requiring medical treatment for children.

"Faith healing practitioners and individuals who believe in faith healing have had a lot more difficult time, if not almost impossible time" defending themselves in the deaths of children, said Steven Green, a Willamette University law professor.

Green, the former general counsel for Americans United for Separation of Church and State, said the legal standard for state intervention in medical care of children had been a "compelling" interest in protecting their health and welfare.

But he said a number of cases and some key Supreme Court rulings have reduced the threshold for intervention since the early 1990s.

"And even when the standard was higher, faith healers were not winning these cases," Green said.

Carter Snead, a Notre Dame law professor and adviser to the President's Council on Bioethics, said judges have also tried to strike a balance over the years between parental rights and faith healing.

"It's a very big deal when the state overrides the parents -- but I completely agree with those who say the state is in the right here," Snead said.