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.
According to Estella Olguin with CPS, this is the fourth child to die in a hot car in Harris County this year. There have been six hot car deaths in Texas -- four in Harris County and two in the Dallas area. For the year, 26 children have died in cars in the US.
Just Wednesday, a three-year-old boy died in a car in Webster when the child's grandmother forgot to drop him off at day care before she went to work. She discovered his lifeless body about 10 hours later.
No charges have been filed in either case.
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