Sisters Brynn Hawkins, 1, and Addyson Overgard-Eddy, 2, were initially described as in "grave" condition after taken to a hospital in Kerrsville by their mother and a 16-year-old boy on Wednesday.
Sheriff's deputies and investigators with Kerrville Police Department determined that the girls had been "intentionally" left overnight in their mother's auto Tuesday night while she visited friends inside the residence, whose location was not specified, the release said. The Sheriff added that Hawkins tried to bathe the girls, but did not immediately take them to the hospital as she reportedly didn't want to get into trouble. The case is being handled by District Attorney Lucy Wilke, who said additional charges could be forthcoming after she reviews the case and facts are presented to a grand jury. Hierholzer went on to say that this was the most horrifying example of child endangerment he has seen in 37 years in law enforcement.
He said Hawkins left her two daughters in the vehicle. Around noon the next day she found them unresponsive in the auto, Hierholzer said.
But "most of them are accidents", Hierholzer said. And she said, 'No, they're fine.
Weather records show the temperatures ranged in that time from the low 70s (about 22 degrees Celsius) to the high 80s (about 31 degrees Celsius).
Both children died Thursday afternoon.
In that case, Parker County Sheriff's Capt. Mark Arnett told CNN that according to the mother, the children were playing in a back room of their home when they disappeared.
Hierholzer said Hawkins had told doctors that the girls collapsed while smelling flowers. She is being held on $70,000 (£54,000) bond. So far, Hawkins has been charged with two counts of abandoning or endangering a child. A 16-year-old boy, who was not identified in the police report, accompanied Hawkins to the hospital.
Hierholzer also told Fox 29 that one witness told officials that while Hawkins and several others were in the house, they could hear the babies crying and someone told her to bring them inside. He said Hawkins has since confessed.