A 21-month-old boy was found on Friday in a vehicle in Booneville, Mississippi, according to a statement from Booneville Police Chief Michael Ramey.
Ramey said although the vehicle was in a parking lot between a daycare and an adult daycare facility, neither were involved in the death.
It appears the child was left in the vehicle at a workplace all day before the car arrived at the parking lot and the child was discovered, Ramey said.
Another child died the same day after being found unresponsive in a vehicle in Lindenwold, New Jersey.
The 22-month-old girl died after she was discovered in a minivan outside a commuter rail station in the Philadelphia suburb around 3:38 p.m., officials said.
It's unknown how long the child was in the vehicle before she was found and no charges have been filed, according to the Camden County Prosecutor's Office.
Onlookers in Lindenwold watched as police wrapped crime tape around surrounding vehicles and draped a tarp over the open sliding door of the van, CNN affiliate WPVI-TV reported.
"My heart just broke," said Ashely Iwu, whose car was enclosed within the police perimeter. "I can barely stand outside and so who can imagine what the temperatures are like in the car -- probably in the hundreds."
Heatstroke kills 38 children every year on average, according to the National Safety Council.
These include instances in which a child has been forgotten in a vehicle, when they accidentally lock themselves in a car or trunk, and in a small number of cases, when a child has been intentionally left in a car.
Since 1998, more than 800 children have died from pediatric vehicular heatstroke, which occurs when a child's body temperature rises to 104 degrees. A temperature of 107 degrees is lethal, according to the National Highway Transportation Safety Administration.\
The majority of heatstroke deaths occur by accident, according to NoHeatStroke.org, a data site run by San Jose University's Department of Meteorology & Climate Science. More than half happen when parents forget about their child in the backseat. Another 26% of children die after entering a vehicle on their own, and about 19% are left there intentionally.
Last year was the deadliest year for child vehicular heatstroke in 20 years, with 52 children between 7 weeks and 5 years old dying after being left in cars, according to Amber Rollins, director of KidsandCars.org, a national nonprofit.