This story has been updated to correct boy’s age.

A 3-year-old boy was killed Tuesday in Charles County when he climbed out of his mother’s car and was hit by an oncoming vehicle, authorities said.

The incident occurred about 2 p.m. in a quiet residential neighborhood in the Waldorf area, the sheriff’s office said.

Based on a preliminary investigation, the boy was in the back seat of his mother’s car in the 10500 block of Sugarberry Street when she apparently spotted the mail carrier and pulled to the curb to hand him some mail, said Diane Richardson, the spokeswoman for the sheriff’s office.

The boy, without his mother’s knowledge, unbuckled himself and got out of the car, Richardson said.

He walked behind the car and into the path of a sport-utility vehicle, Richardson said. It happened “in the blink of an eye,” she said.

The names of those involved were not immediately released. Richardson said the woman lives in the general area of the incident, as does the driver of the SUV.

Residents of the street where the incident occurred said in interviews Tuesday night that they did not know any of those involved.

The area is about two miles northwest of the downtown section of Waldorf and is known as Autumn Hills, the residents said.

The slightly curving street where the incident occurred appeared barely wide enough for two cars to pass in opposite directions.