A 3-year-old who was left in his mother's truck in 90-degree heat as she worked her shift at a Houston hospital died after wriggling free from his car seat, climbing into the front seat and apparently trying to start the ignition or open the windows, officials said.

Cameron Thomas Boone is the second child to die in a locked, hot vehicle in the Houston area within less than 24 hours. Temperatures reached 94 degrees Thursday.

Sheriff's Lt. John Denholm said the boy's mother found him unconscious when she returned to the truck after her shift at North Cypress Medical Center about 3:30 p.m.

She broke the back windshield and called for help, but the child was dead when she brought him into the hospital emergency room. Authorities said she used a rock to break the windshield because the remote door locks with a key already in the ignition.

Denholm says the woman had meant to drop the child off at day care but had forgotten he was in the truck.

Denholm said the hospital had security guards patrolling the lot, but the truck had tinted windows and it was difficult to see inside. The key found in the truck ignition may not necessarily have belonged to the vehicle, he said.

Denholm would not disclose the mother's position at the hospital. Calls made to the hospital were not returned Friday.

Another 3-year-old boy died in a hot vehicle in Houston late Wednesday afternoon.

No charges have been filed in either case.

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