25-year-old Cynthia Randolph initially said her two-year-old daughter and 16-month-old son locked themselves in the auto, but admitted Friday she locked them in.
Cynthia Marie Randolph, 24, was charged Friday with two first-degree felony counts of injury to a child causing serious bodily injury.
When she told them to get out and they refused, Randolph "shut the auto door to teach Juliet a lesson, thinking she could get herself and her brother out of the vehicle when ready", the statement said.
Randolph allegedly then went inside the house, smoked marijuana and fell asleep for two to three hours. Temperatures that day reached into the mid-90s. As of late Friday, Randolph's bond had not been set.
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Randolph repeatedly changed her story under questioning and told a Texas Ranger on Friday that she had found Juliet and Cavanaugh playing inside the vehicle, the sheriff's office said in a statement.
When the deputies initially spoke to Randolph, she told them she was busy folding laundry and watching television and they were playing in the enclosed back porch when she saw they had disappeared.
But Randolph later admitted to authorities that she left the kids in the auto.
Ms Randolph initially said they were exposed to extreme temperatures inside the vehicle for no longer than an hour.
The pair were pronounced dead from suspected extreme heat exposure and the manner of death in each child is pending, according to the Telegram. Through multiple interviews with investigators over the past month, Randolph "created several variations of the events" of May 26, police said.
A ruling on the cause and manner of death in each child is pending, according to the medical examiner's website.
When she woke, she went to check on the children and found them unresponsive.
Fowler said that any incidents involving any child are hard ones, but this call was especially heartbreaking because of the unfortunate deaths of the two children.