HOUSTON - A 5-year-old boy died Monday after his mother left him in a hot car for up to three hours. 

The Harris County Sheriff's Office said deputies found the child dead in the driveway of a home in Harris County around 3:20 p.m. Monday. 

Officials told KTRK that the boy's mother had gone to a party store with him and her 8-year-old daughter. The mother said she was in a rush to get prepared for the girl's birthday party, and when they returned home she got out of the car without realizing the boy was still strapped to his seat in the back. 

Investigator said the boy reportedly knew how to unbuckle his own seat, and the suspect the mother may have assumed he got out of the car on his own. 

Officials also said the vehicle was loaned to them and unfamiliarity with the safety locks may have been a factor.

The sheriff's office has not said whether the mother will face charges.