A Georgia foster mother has been charged with two counts each of second-degree murder and cruelty after 3-year-old twins died in a hot car.

Raelynn and Payton Keyes, age 3. Family photo

Claudette Foster was charged Oct. 14, about two weeks after the deaths of Payton and Raelynn Keyes, Hinesville police said. The girls were in Foster's care when they were found unresponsive in the backseat of a car in Hinesville, about 40 miles southwest of Savannah, on Sept. 29.

Police said Foster was charged with murder in part because she was negligent while taking care of the twins.

The girls had been missing for hours before they were found unresponsive in the car at the home of Foster's fiancé, Whitney Morris, public relations manager for the city of Hinesville, told NBC News.

Police determined that there was a lack of supervision that allowed the preschoolers to get in the vehicle and pass away, Morris said.

Foster parent Claudette Foster. Lewis Levine, Coastal News Service / via Hinesville Police Department

Preliminary autopsy results indicated the children died from accidental heatstroke, police said.

Foster turned herself in to police Oct. 14. She is being held at the Liberty County Jail awaiting her first court appearance, according to police and jail records. It was unclear if Foster has an attorney.