Crowley police said they arrested Deborah Reece, 60, and charged her with felony child endangerment after she left her 2-year-old grandchild in her vehicle while she shopped.
Police said two women approached an officer carrying the child in the Walmart parking lot at 1221 E. Farm-to-Market Road 1187 at about 5:40 p.m. Monday.
They told police that they heard screaming when they parked and saw the child in the next vehicle belted into a safety seat with the windows up and the car not running.
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The women told the officer that they waited by the vehicle for a few minutes and then opened the door and removed the child, police said.
Police said they identified Reece as the driver of the vehicle when she returned to the vehicle with several bags of groceries. Using the store surveillance video, they determined that the child was in the vehicle for nearly an hour.
The grandmother reportedly told police she forgot the child was with her.
"She informed the officers that when she went into the store, apparently, the child was sleeping and quiet and she didn't realize that the child was in the vehicle," said Crowley police officer C.C. Meadows.
Police said emergency responders treated the child for prolonged heat exposure and took her to Cook Children's Medical Center for further evaluation.
That child has since been released, according to police.
Viewer comments posted on the NBC DFW Facebook page alerted the news department to a sign posted on the automatic glass doors at the entrance to the Walmart that reads, "Look Before You Leave: Please make sure children are not left unattended in vehicles."
Reece bonded out of the Crowley jail Tuesday evening, hiding her face and saying nothing to reporters as an officer escorted her to her husband's waiting truck.
Earlier in the day, Reece's adult daughter came to visit her mother in jail with the 2-year-old child in tow.
Family members refused to offer any statement or explanation to reporters.
NBC 5's Todd L. Davis contributed to this report.