On Thursday, the boy in Houston entered the car parked near a house to retrieve his toy from the back seat, said Kese Smith, spokesperson of the Houston Police Department. He entered through the unlocked front door and climbed into the back seat.
Once he got into the back seat, he couldn't open the back door because the child protective locks were on, Smith said.
Since 1998, more than 660 children across the United States have died from heatstroke when unattended in a vehicle, and 29% of those kids were playing in an unattended vehicle or gained access on their own, said Amy Artuso, a program safety manager for the National Safety Council.
The council advises parents to keep vehicles locked and keys out of reach of children while teaching them that vehicles aren't safe places to play, Artuso said.
"If your children are locked in a car, get them out as quickly as possible and dial 911 immediately." she said.
Family members found the boy in the back of the car, about 30 to 45 minutes after he was last seen. He was in cardiac arrest and a family member began performing CPR.
A 911 call was made around 2 p.m. The boy was taken to the Lyndon B. Johnson Hospital, where he later died, according to the Houston Fire Department.
Police are still investigating but the Houston death appears to be a tragic accident, Smith said. It was extremely hot in Houston on Thursday, with a high of 100 degrees.
Artuso said the death could have happened in practically any state in the summer.
"As a reminder, due to the way vehicles heat up -- like a greenhouse effect -- this tragedy can happen in any state, and cracking windows does not make a significant difference to decrease the internal temperature inside a vehicle," Artuso said.
The council reported last week that nearly three times as many children have died
after being left in hot cars this year compared to that time last year.
Georgia man accused of murder in hot-car death
While no charges have been filed in the Houston case, a Georgia man is set to to go to trial soon in the case where prosecutors say they believe he used a hot car to kill his toddler son in metro Atlanta.
CNN-affiliatte WSB reported
Thursday that a judge has picked the city of Brunswick in south Georgia as the location for the Ross Harris' murder trial,
Superior Court Judge Mary Staley granted a motion in May t
o move the trial out of Cobb County because of excessive publicity about the case in metro Atlanta
Harris is accused of leaving his young son to die
in a hot SUV.