A 6-year-old girl was killed Monday night while playing in a sandbox in front of her Beltsville house when a salesman leaving the house backed his car into the child and then left the scene, according to police and family members.

According to family members, the child, Dawn Hinton, was found on the lawn near the sandbox about eight to 10 minutes after a salesman had backed his car out of the driveway on Edmonston Road after trying to sell a car battery to one of the family members.

The salesman was detained by Beltsville police yesterday for questioning, a police spokesman said. Police would not identify the driver.

Police officials said it was unclear whether the driver, who left the house about 8 p.m. Monday, knew he had struck the child.

Family members, however, said they believed the man could not have been unaware he had run over the child.

"He drove onto the grass and then hit the sandbox before he hit her. From where she was when I found her, there was no way he could not have known he hit her," said John T. Hinton, Dawn's uncle, who also lives at the Edmonston address.

Hinton said that the salesman had visited the house several times in the last few years in an attempt to buy or sell used products.

"He tried to sell us some other stuff before. He drifts in and out and tries to sell things to make money," Hinton said. " . . . He comes over whenever he needs money or whenever he is trying to buy something. He was unwanted around here."

"Yesterday, before he left, he tried to sell me the car he had run her over with," he said.

Although details remain sketchy, family members said the salesman was forced to back out of the circular driveway in front of the house because other cars were blocking the forward path. He apparently backed onto the grass about 25 feet, ran over the child, and then drove off, Hinton said.

About 10 minutes later, Hinton said, he came out of the house and noticed Dawn lying on the ground near the sandbox.

"When I went out and saw her, I thought she was playing with me," Hinton said.

Dawn, who was described by family members as an intelligent and playful child, was about to begin her first year of grade school at Beltsville Elementary School.