As temperatures across the country rise, so to have the number deaths of children left or trapped inside sweltering automobiles.
Eighteen children have died across the country since the beginning of the year, eight of them in just the past 12 days, a record setting number of deaths for the first six months of the year since such data began being collected in 1998.
Since 1998, 463 children have died of overheating or hyperthermia in cars in the United States, the majority of whom were accidently left behind by caregivers.
This year's deaths, however, have been marked by an increased number of unattended children who became trapped while playing inside a hot car, said Jan Null, a meteorologist at San Francisco State University who tracks hot car deaths.
"These are epidemic numbers. Unlike a lot of epidemics, every one of these deaths is preventable," Null told ABCNews.com. "There is no reason children have to die this way."
According to Null's data, 33 children died last year in hot cars, slightly below the annual average of 37 children, but it is not yet known if this year will be any worse than years past.
Less than one week since the official start of summer, this June is one of the deadliest on record. Hot car deaths typically spike in July, according to Null. With a week left in June, the number of deaths has topped the previous high of 17 fatalities from January to June 2009.
Young children are particularly susceptible to hyperthermia, said Dr. Gary Smith, director of the Center for Injury Research and Policy at Nationwide Children's Hospital in Columbus, Ohio.
"The inside of a car on a hot day heats up incredibly high and quickly," he said. "In a short time, temperatures of 120 to 140 degrees can occur."
The heat overwhelms a child's ability to regulate his core temperature and the child quickly loses consciousness, Smith said.
"When a kid is in a hot car, he is gaining heat very quickly and there is no way to get that heat out of their bodies. The mechanisms for compensating are overwhelmed and their core temperature rises. The child becomes unconscious and brain damage occurs. A kid left even for a half hour can become unconscious and unresponsive," he said.
Historically most children, 51 percent, who die in hot cars are accidently left there by a parent, Null said.
"It was basically an accident," Melody Costello told ABCNews.com, about how her 4-month-old son Tyler died when his father parked his car in the office lot and left the baby inside for three hours in 2002.
Todd Costello, Tyler's father, typically did not drive the baby to the babysitter in the morning, and that small change in routine led him to forget the quiet baby in the back seat of his Dodge Neon.
"It was 94 degrees that day and the car registered 120 degrees. Tyler's body temperature was about 108 degrees when they found him," she said.
The Costellos have since had another child, a son who is now 6. The couple call each other each time one is scheduled to drop off one of their two children to make sure the kids are accounted for.
This year, Null said, a surprising number of the deaths involved children who died while playing unsupervised inside a car they were unable to escape from.
On Monday a 2-year-old boy, Hunter Iles was found dead in the passenger seat of his family's car after playing with other children outside his home in Hineston, Ala.
A week earlier, 2-year-old twins llannah and Alliya Larry were found dead in their grandmother's car on June 16.
In both cases outside temperatures were in 90s.
Experts said hot car deaths were preventable with simple precautionary steps.
To prevent children from dying while playing in a car, parents should "absolutely keep their cars locked even if in the garage or driveway. That's where these accidents take place," said Janette Fennell, founder and president of KidsandCars.org, an advocacy group.
"Children should not have access to keys and key fobs. They love pushing that button and hearing the car beep," she said.
Parents should create routines that remind them their child is still in the car, she said.
Keep a stuffed animal in the car seat, Fennell suggested. When you place the baby in the seat, move the doll to the front passenger seat, to remind you the child is in the back, she said.
Parents should also leave their cell phone, employee ID, handbag, or another item they will need, on the floor in front of the baby's car seat. "It's important parents always get in the habit of opening the back door and checking they have the baby," Fennell said.