No charges have been filed in the case of a Blacksburg toddler who died Friday after being left for an entire workday in his mother's parked car, but heat stroke has been confirmed as the cause of death.

Dr. Amy Tharp of the Roanoke medical examiner's office said Wednesday that the child, whose name The Roanoke Times is withholding at this time, died of acute hyperthermia, also known as heat stroke. Standard toxicology test results are pending and a full report will take more time, Tharp said.

Blacksburg police have been reticent to release many details of the case. But Jan Null, a California-based expert in vehicle-related heat deaths in children, said police told him the mother of the child, who was not yet 2 years old, likely forgot to drop the child off at Rainbow Riders day care center before going to work Friday morning.

The mother found the child unresponsive in her car about 5 p.m., after arriving back at the day care center on Ramble Road, where she expected to pick up the child.

"With an outside temperature of approximately 88 degrees on Friday, the inside air temperature of the car would have been in excess of 130 degrees," said Null, a meteorologist and adjunct professor at San Francisco State University.

Under those conditions, a small child can succumb to the heat in as short a time as 15 minutes, Null said.

According to a police news release, the mother took the child into the center, where day care employees administered CPR and called 911. The child was pronounced dead at the scene. It was the second such child death to occur in Virginia this year, Null said.

The mother's employer held a prayer meeting for the family and has provided counselors for workers. Extensive counseling services have also been offered at Rainbow Riders, head administrator Kristi Snyder said Wednesday.

The mother was not an employee of Rainbow Riders, but the family had been affiliated with the center for about five years, and, according to Snyder, "their world revolved around their children."

The deceased toddler is not the family's only child.

Snyder called the death a "horrible accident" and said those at the center are grieving with the family, whom the teachers and administrators hold in "high regard," she said.

Wythe County Commonwealth's Attorney Gerald Mabe has been named a special prosecutor in the case. Montgomery County Commonwealth's Attorney Brad Finch said this week that he recused himself because he has a relationship with the child's family.

Mabe said Wednesday that he expected to confer with Blacksburg police soon. But it's unclear if any charges will be filed.

Recent studies conducted by The Associated Press and Wake Forest University family law professor Jennifer Collins reveal wide disparities in criminal prosecution of these incidents. Some of the statistics indicate sex and class bias often play a role.

Both studies show that mothers of the children are charged more often than fathers. Collins' 2006 study of data from 1998-2003 showed that in 130 cases, 60 percent of mothers were charged, compared with 44 percent of fathers. AP data published in July shows that mothers are often given longer jail sentences.

"I think we tend to hold mothers to a higher standard, both in life and in the criminal justice system," Collins said.

But family income seems to be a strong indicator of who will be charged in the deaths of children left in parked cars. Of the 51 cases where Collins could ascertain the socioeconomic status of the parents involved, only 23 percent of those who could be classified as white collar were charged, compared to 85 percent of parents who could be classified as lower income.

Other factors can lead to prosecution, including alcohol or drug use by a caregiver or parent, or a history of abuse or neglect, Collins said. Overall, about half of parents are not charged, however.

Last week in a high-profile incident, Ohio authorities declined to press charges against a school administrator whose 2-year-old daughter died after being left for hours in the mother's car in a school parking lot.

In 1990, Roanoke prosecutor Donald Caldwell declined to charge a Botetourt County mother whose 2-year-old daughter died in a vehicle. Caldwell was quoted at the time as saying "I don't think that society could punish her any more than she's already punished herself."

The AP study shows that paid caregivers, however, are more likely than parents to be charged for forgetting a child in the back seat.

Two years ago a Roanoke County Department of Social Services aide was found guilty of reckless endangerment of a child and lost her job after she left a 10-month-old in a county vehicle. The child was found unhurt after five hours.

But across the country each year about 36 children on average -- most of them younger than 4 -- die of heat stroke in parked vehicles, Null said.

Staff writer Laurence Hammack contributed to this report.