A 6-year-old boy is in critical condition after he was struck by a passing car while sledding on a steep driveway of a vacant home that is for sale in McLean. (Antonio Olivo/The Washington Post)

A 6-year-old boy was listed in critical condition Wednesday after he was struck by a passing car while sledding on a steep driveway in McLean.

Fairfax County police said the incident occurred about 5:40 p.m. The boy was part of a small group of children who were under adult supervision and were snowboarding and sledding at a property in the 7000 block of Matthew Mills Road.

The boy’s sled slid into a 2015 Lexus as it passed on the street, police said. The driver of the car, a 65-year-old McLean woman, heard a loud noise, according to a police news release. She recognized what had happened and “immediately got out and rendered aid to the child.”

The driveway is on the property of a vacant house that has a for-sale sign posted. Esfandiar Khazai, a developer who lives near the other end of the block, said children often go to the empty house to play. Although they are supervised by adults, it still worries him.

“They’re always doing that,” Khazai said. “I’m always very careful when I pass.”

The boy was flown to Inova Fairfax Hospital with life-threatening injuries. In a Thursday morning news release, police said the boy remained in critical condition. The driver was not injured.

“It is a very sad reminder that an extremely serious injury like this can just happen so fast,” said Lucy Caldwell, a spokeswoman for Fairfax County police.

Police had said the boy was snowboarding but later said they determined he was riding a “flat-bottom sled.”

No charges have been filed against the driver. Police said speed and alcohol were not factors in the crash, which remains under investigation.