WASHINGTON — (CNN) An 18-month-old girl was found dead in the family car Sunday afternoon in Abilene, KS.

A Johnson County non-profit that tracks deaths related to children and cars says Olivia Engstrom is the 24th child in the United States that has died this year due to heat stroke in a vehicle compared to 12 children last year at this time.

Dickinson County Sheriff Gareth Hoffman says the toddler was playing outside her parents’ rural home with several siblings.

The adult in charge at some point noticed she was missing from the group, and by the time someone checked the car, she was not breathing.

It was 6:15 p.m. when someone contacted the sheriff’s office. Olivia was pronounced dead at the scene.

A similar set of circumstances led to the death of a 2-year-old boy the weekend prior in the southeast Missouri town of Rocky Comfort.

“These aren’t bad parents that this happens to,” said safety advocate Amber Andreasen. “We work with a lot of them. Many of them really thought that their child was safe.”

Andreasen is the director of KidsAndCars.org, a national organization based in Olathe.

She says toddlers are curious by nature, they might consider trunks and floorboards good hide-and-seek hiding spots, but just because a youngster can get in on their own, doesn’t mean they grasp getting out.

“When a child gets in that heat is so strong that they really are overcome within minutes and don’t have cognitive ability to understand what’s making them feel really bad,” said Andreasen.

July brought eight child deaths in the U.S. caused by children left in hot vehicles.

Seven of them were due to the children getting into the vehicles on their own.

Andreasen says even those who don’t have kids can save lives by getting into the habit of always locking their cars.

“A lot of times children will crawl into a neighbor’s car, and parents don’t think to look for them there,” said Andreasen.

For the same reason, she advises parents and those caring for small children to keep their car keys out of reach.

If a child goes missing, she says, vehicles and car trunks should be the first place to check, not just yours but neighbors’ cars as well if you live in close proximity to your neighbors.

She suggests people think of their cars in much the same way as they might think of a pool.

“If your child went missing, your mind would go straight to that pool and you would check there right away,” said Andreasen. “The same thing is with a car. A few minutes can be the difference between life and death.”

Sheriff Hoffman says Olivia Engstrom’s parents were home the whole time.

He didn’t know how long she had been in the car or how she got in.

He would not speculate on the likelihood of charges but said Monday that he considered her death a tragic accident.

“I think it’s one of those situations where we have to all be mindful of what matters most to us,” said Hoffman, “and that’s obviously our children.”

Asked why the 2016 data to date on child heat deaths in cars showed such a sizable increase from the previous year, Andreasen didn’t have a concrete theory.

She said one factor is that the number of deaths in 2015 stood out as unusually low.

The highest number since the organization started keeping track in 1990 was 49 deaths.

From 1990-2015, the scenarios related to deaths of kids in hot cars rank children getting in on their own as the second most common:

•54 percent left in car unknowingly

•33 percent got into car on own

•12 percent left in car knowingly

•1 percent unknown

Of the eight deaths in July, 2016, just one involved a parents accidentally leaving a child behind in a car.

The 2-year-old boy died inside the car in Texas while he family was inside for a church service.

The other seven were children getting in on their own:

•July 6, Ohio, 3-year-old boy

•July 10, Texas, 2-year-old girl

•July 15, Florida, 2-year-old boy

•July 22, Florida, 3-year-old boy

•July 22, Pennsylvania, 4-year-old girl

•July 23, Missouri, 2-year-old boy

•July 31, Kansas, 18-month-old girl