When Amanda Hawkins arrived at Peterson Regional Medical Center in Kerrville, Tex., her two daughters were in grave condition.
As Ms. Hawkins told it, she and the toddlers had been at nearby Flat Rock Lake when one of the girls, then the other, collapsed. She wondered aloud whether the children, who she said had been smelling flowers, had come into contact with something poisonous.
The girls died Thursday at a hospital in San Antonio. On Friday, the authorities in Kerrville, about 65 miles northwest of the city, painted a very different picture of events than Ms. Hawkins had described.
The Kerr County sheriff, Rusty Hierholzer, said Ms. Hawkins, 19, had intentionally left the girls — Brynn Hawkins, 1, and Addyson Overgard-Eddy, 2 — in her car for more than 15 hours while she was at a friend’s house.
“This is by far the most horrific case of child endangerment that I have seen in the 37 years that I have been in law enforcement,” Sheriff Hierholzer said in a statement.
Ms. Hawkins was arrested on two counts of abandoning or endangering a child. She was being held late Saturday at Bexar County jail in San Antonio awaiting transfer to Kerr County.
Sheriff Hierholzer said the charges could be upgraded after the case is presented to a grand jury.
He said Ms. Hawkins left the children in her vehicle on Tuesday night, outside the home of a friend she was visiting, and did not return to them until around noon Wednesday. Temperatures rose into the 90s on Wednesday morning, Sheriff Hierholzer told Fox 29 in San Antonio.
A 16-year-old boy who accompanied Ms. Hawkins to the house went out to the car with the children for “a little while,” but returned inside, Sheriff Hierholzer told Fox 29. He will “probably have to face some charges,” the sheriff said. “He does have some culpability in this.”
The sheriff told Fox 29 that someone in the house had apparently heard the children cry out and told Ms. Hawkins to bring them inside, but she did not.
After finding the children on Wednesday, Ms. Hawkins tried to bathe them, Sheriff Hierholzer said in his statement. At first, she did not want to take them to the hospital because “she didn’t want to get into trouble,” but later she made up the story about the trip to the lake, he said.
Once medical personnel in Kerrville recognized the seriousness of the girls’ condition, they transferred them to University Hospital in San Antonio. They were taken off ventilators and died around 5 p.m. Thursday, Sheriff Hierholzer told Fox 29.
The Bexar County medical examiner’s office was scheduled to conduct autopsies on Friday. Officials there could not be reached on Saturday night to discuss the results.
It was not clear whether Ms. Hawkins had a lawyer.
In an interview with The San Antonio Express-News, Alisha Eddy, who the newspaper identified as Ms. Hawkins’s mother, said, “I don’t agree with what happened,” but added, “I love my daughter. I’m there for my daughter.”
A woman who answered the phone on Saturday at a number listed for one of Ms. Hawkins’s relatives said, “We had two babies in our family die this week — we’re not talking to anyone,” before hanging up. She did not identify herself.
So far this year, 11 children in the United States have died of heatstroke after being left in cars, according to Jan Null, a meteorologist at San Jose State University in California who tracks such deaths on noheatstroke.org. There were 39 such deaths last year, according to the site.
Sheriff Hierholzer said most were because of some oversight.
“These children were left in that car intentionally,” he told Fox 29.
“Helpless little kids,” the sheriff said. “And it was totally preventable.”