The Houston Police Department said they got a call around 12:25 a.m. Monday regarding that car in the 2400 block of Windbern Street.
A tow truck driver noticed the sleeping child when he came to remove the vehicle.
Court documents say the child's mother, Brandy Brown, was drinking at a club in the 2400 block of Wheeler Avenue as this was taking place. She has been charged with endangering a child.
The 3-year-old boy wasn't injured and was picked up by an uncle, according to a spokesperson with the Houston Police Department.
Court records show Brown was convicted of a DWI charge last month and had a suspended license at the time of this arrest.