Randolph initially told police the children, 1-year old Cavanaugh Ramirez and 2-year old Juliet Ramirez, had locked themselves in the vehicle.
Cynthia Marie Randolph, 24, was charged Friday with two first-degree felony counts of injury to a child causing serious bodily injury.
The incident occurred near Lake Weatherford, Texas, located about an hour west of Fort Worth.
Authorities said Randolph initially told officers that she had been folding laundry in the house while her children played outside.
Parker County Sheriff's Department investigators arrested Cynthia Randolph after admitting that she left her kids in the vehicle to "teach them a lesson". When her daughter refused, she shut the door, but believed the children would figure out how to get out when they've learned their lesson.
Unfortunately, as the North Texas temperatures soared to the mid-90s and Randolph reportedly said she went inside to smoke marijuana, little Juliet was not able to escape the vehicle with her brother.
According to records, Randolph is now held at the Parker County Jail on a bond of $200,000. The website noheatstroke.org says humans enter heat stroke - a potentially fatal condition - at 104 degrees.
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The children were pronounced dead about a half-hour after authorities were notified.
She looked into the room they had been playing and noticed they were gone.
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.
Authorities were called to the home at about 4 p.m. when the mother said she had discovered them unresponsive in the vehicle.
The Parker County Sheriff's Office has arrested Cynthia Marie Randolph after further investigation into her children's "accidental" death revealed that it was actually a deadly lesson she subjected the toddlers.
No bond has been set yet in her case.