The Texan woman, Cynthia Marie Randolph, 24, initially told investigators her two-year-old daughter and 16-month-old son locked themselves in the auto on May 26.
Cynthia Marie Randolph, 24, was being held Saturday on two counts of causing serious bodily injury to a child.
In Randolph's initial statements, the sheriff's office told NBC 5, she said the two children had been playing and when she couldn't find them in the house, she started searching the property, eventually locating them in the vehicle. The Parker County Sheriff's Department determined that Randolph changing her story about how her children died was probable cause for arrest.
She also stated that after she left the children in the auto with the doors shut, she went inside her residence, smoked marijuana, and after getting high, took a nap for several hours. Temperatures that day reached into the mid-90s.
"Please send a thank you to [the] Parker County Sheriff's Office and the Texas Rangers from the Ramirez family", the statement said.
When Randolph found the children in distress, police said the woman broke the window of the vehicle to make the incident "look like an accident".
The toddlers died in the vehicle. After she found her children unresponsive, she called the authorities, who arrived on the scene at around 4 p.m.
But she eventually admitted that she had found children playing in the vehicle at about 12:15 on that day.
In initial interviews with investigators, the Parker County Sheriff's Office says Randolph claimed she was in her home west of Ft Worth on May 26 when she noticed her children were missing. She initially told authorities she was folding laundry and watching TV as the children played on an enclosed porch. Randolph will go before a judge for a bond hearing and more details will be revealed regarding the charges she'll face. She fell asleep for two or three hours.