An awful milestone was reached this past weekend.

Eight hundred children have died in hot cars since records began in 1998, according to NoHeatStroke.org.

The 800th child to die was a 4-year-old boy in St. Paul, Minnesota, who was found dead Saturday after he was left alone for hours in a hot SUV while his father was at work.

Dozens of children will be dead in hot cars by the end of the summer, if past years are any guide.

On average, 38 children die while trapped in hot vehicles every year, according to Jan Null, an adjunct professor of meteorology at San Jose State University. Last year, a record 52 children died.

Null said that aside from crashes, heatstroke is the leading cause of death in vehicles for children 14 years old and younger.

Cars transform into ovens when direct sunlight heats objects inside. Temperatures can soar to 120 or 130 degrees even when the outdoor temperature is only in the 80s. The body's natural cooling methods, such as sweating, begin to shut down once the core body temperature reaches 104 degrees. Death can occur at 107 degrees.

Children are particularly vulnerable because they have difficulty escaping a hot vehicle on their own, and their respiratory and circulatory systems can't handle heat as well as adults.

July is usually the deadliest month for children in overheated cars. It had the highest toll of 16 deaths in 1999, Null said. "The warmer months are the biggest variable, but in summer months, people’s routines are changed, so that could be a contributor," Null said last year.

Since the mid-1990s, the number of children who died from heat exhaustion inside vehicles has risen dramatically.

The requirement for children to sit in back seats after juvenile deaths from air bags peaked contributed to the climb since children are more easily forgotten in the back seat than the front.

Forgetting a child in the car can happen to anyone, Arizona State University psychologist Gene Brewer said last year.

“Often these stories involve a distracted parent,” Brewer said. “Memory failures are remarkably powerful, and they happen to everyone. There is no difference between gender, class, personality, race or other traits. Functionally, there isn’t much of a difference between forgetting your keys and forgetting your child in the car.”

In Minnesota on Monday, Kristopher Taylor, 26, of Apple Valley, was charged with second-degree manslaughter in the death of his son.

The temperature reached 70 degrees Fahrenheit, and the criminal complaint says the boy was in the sun.

Another child in Lakewood, New Jersey, died in a hot car on Monday, bringing the yearly total to 6 and the 20-year total to 801, according to NoHeatStroke.org.

Contributing: The Associated Press