Cynthia Randolph, 24, was being held on Saturday on $200,000 bail for the deaths of her 16-month-old son and 2-year-old daughter last month, Danie Huffman, a spokeswoman for the Parker County Sheriff's Office, said in an email.
Randolph had originally told investigators that she had been folding laundry and watching television in her rural home west of Fort Worth while the boy, Cavanaugh Ramirez, and his sister Juliet Ramirez played in a back porch, according to a criminal complaint.
After noticing the children were missing, Randolph told officers she found them unresponsive in a locked car and broke a window to rescue them. The temperature was close to 96 Fahrenheit (36 Celsius) and emergency personnel that Randolph had called pronounced the children dead at the scene, the court filing said.
Randolph repeatedly changed her story under questioning and told a Texas Ranger on Friday that she had found Juliet and Cavanaugh playing inside the car, the sheriff's office said in a statement.
When she told them to get out and they refused, Randolph "shut the car door to teach Juliet a lesson, thinking she could get herself and her brother out of the car when ready," the statement said.
Randolph went inside the house, smoked marijuana and took a nap for two or three hours. When she awoke, she found the children unresponsive inside the car and broke the window to make it look like an accident, the statement said.