Police yesterday were investigating a fatal Charles County sledding accident to determine where exactly a car struck a sled carrying three children along a snow-cloaked road Monday night, and whether anyone was responsible.

Jeremy C. Caleco was riding with his two half-siblings on a sled being pulled behind an all-terrain vehicle by their stepfather just after 6 p.m. Monday when a Honda Accord swerved off Route 6 in southern Charles and struck the sled, the Maryland State Police said.

At the time, a sheet of snow covered the ground along the rural road in Charlotte Hall, making it difficult to tell the boundaries of the road. Authorities are trying to determine whether the ATV was on, or just very near, the road.

The driver of the Accord, Andrew P. Rutter, 29, of La Plata told police that he believed the ATV was coming at him head-on, so he swerved, making him lose control, go off the road and hit the sled, said 1st Sgt. Daniel Truitt.

No charges had been filed yesterday.

"It's just an unfortunate tragedy, with some people playing too close to the roadway," Truitt said.

The children's stepfather, Tony B. Sherman, 43, was driving the Yamaha Big Bear ATV, pulling the children west, parallel to the road, while the Accord was traveling east, police said.

They "were just out having family fun," said Sherman's son, Chris Sherman, 16.

Tony Sherman was not injured in the crash. Christiana G. Zell, 11, was taken to Children's Hospital in Washington, where she is in critical condition with a blood clot in her brain, police and relatives said. Joseph A. Zell, 10, was treated for minor injuries.

As the snow melted yesterday, Charles sheriff's officers and members of the Maryland State Police examined the scene and the circular tracks of the ATV still visible on the snow-covered lawn along Dubois Road.

"It's illegal [to ride an ATV] on the roadway," Truitt said. "To do it on private property -- I don't know that that's illegal. It's obviously not a real good idea. He was very close to the edge of the road."

The three children attended Dr. Thomas L. Higdon Elementary School in Newburg, where Jeremy was in kindergarten, Joseph is in fourth grade and Christiana is in fifth grade. At the school yesterday, classmates made cards for the family, Principal Peggy E. Mertes said.

Mertes described Jeremy as a smiling, happy boy who was known far beyond his grade.

"He was a very distinct personality, very vivacious. He was infectious," she said.

Jeremy often talked about his interest in angels and would frequently rush to administrators with new bits of cleverness. The day he died, he came to Vice Principal Wilhelmina Pugh holding out a calculator.

"Mrs. Pugh, this is for you!" he rhymed, according to Mertes.

"He never seemed to walk -- he seemed to glide through the school. He was just a go-getter," Mertes said. "He just endeared himself to everybody."