Police are calling the death in Springfield, Virginia’s 93-degree heat a "tragic accident," FOX 5 in Washington, D.C. reported.
The child may have been left in the car for "several hours" after being driven home with other family members. Investigators were trying to determine why the child was forgotten.
The child was given CPR and was pronounced dead at a hospital, FOX 5 reported.
"Our heart breaks for this family," Fairfax Police Lieutenant John Lieb said, according to WUSA-TV in Washington, D.C.
Already this year, 11 children have died in hot cars across the country, according to advocacy group Kidsandcars.org.
The $1.2 trillion bipartisan infrastructure bill that passed the Senate on Tuesday includes a section that would require the National Highway Traffic Safety Administration to mandate "that new cars come equipped with technology to alert the driver to check the back seat when the car is turned off," WRC-TV in Washington, D.C. reported.
The technology "would allow states to use federal funding to educate the public on the dangers of leaving a child unattended in the backseat of a car, and requires the Department of Transportation to study options for retrofitting existing vehicles to address the problem," U.S. Sen. Richard Blumenthal, D-Conn., said in a statement, according to WRC.