It was a parent's worst nightmare.

On a sunny Easter Sunday afternoon, 7-year-old Carl Ellis Arthur headed out on his bicycle from his home in Southeast Washington. On a playground across from his house, he met two 12-year-old boys, and they headed for Oxon Cove, near the Oxon Hill Children's Farm and the Potomac River.

At water's edge, according to authorities, the two older boys attempted to steal Carl's bike, hit him with a baseball bat, pushed him into the water and pelted him with stones and debris until Carl drowned.

Yesterday, the two 12-year-old District youths were charged as juveniles with the assault, robbery and murder of the boy, who lived at 4184 Livingston Rd. SE. Prince George's County juvenile court authorities ordered the boys held in a Maryland children's facility until their scheduled trial May 6, which would have been Carl's 8th birthday.

U.S. Park Police said they did not believe that Carl, a first grade student at the Friendship Educational Center, knew the two boys, whose names were being withheld by authorities because of their age.

Carl apparently met the boys, one from Southeast Washington and the other from Northeast, about 11:30 a.m. in the playground portion of the federally owned Oxon Run Park near Carl's apartment complex, according to Lt. Bill Frazier, head of the Park Police criminal investigations unit.

Frazier said the younger child accepted an invitation to ride with the older boys along a path to Oxon Cove where, he said, they decided to steal his bicycle. About noon, he said, one of the boys hit Carl in the head with a small, wooden baseball bat then pushed him into the water.

Frazier said the police investigation showed that the boys "continued the assault by throwing rocks and other debris at him . . . . The water was shallow, but the child continued to back up until he stepped into water over his head."

One of the boys told his father about the incident Sunday night, Frazier said, prompting the father to call the District police. About an hour later, shortly after 9 p.m., the District police harbor unit found Carl's body in Oxon Cove, down a hill from the Oxon Hill Children's Farm.

Carl Arthur was known to neighbors as "Eric" and to his family as "Meatball." He lived with his mother, Diana Arthur, a brother, Greg, 14, and a sister, Shermeka, 2, at the Livingston Road address.

In an interview with WDVM-TV (Channel 9), Diana "Peaches" Arthur said she was still trying to understand how her son had died. "He had to have known them the boys because he don't deal with strangers."

Deborah Wood, the boy's aunt who also lives in the apartment, said yesterday that the family wondered about Carl's whereabouts "when we went to look for him for a late breakfast . . . about 1 or 2 in the afternoon ."

Wood said family members continued looking for the child Sunday evening but did not call police.

The two boys charged in the death were represented in yesterday's hearing in the county courthouse in Upper Marlboro by the Prince George's public defender's office. Elvira White, the attorney for one of the boys, said she was not sure he fully understood the proceedings. She said the boys' families were "still very, very distraught."

Court authorities would not release the names of the children charged in the crime yesterday because they are too young to be tried as adults. In Maryland, children must be 14 to be charged as adults in serious crimes. Under juvenile court proceedings a judge will determine at the trial if the two youths are responsible for Carl's death. If so, the judge will decide what type of punishment or supervision they require. Court authorities said they did not believe that the boys had been in trouble before.

The public school Carl attended near his home was closed yesterday for the spring break. His teacher, Jacqueline Banks, said, "At the same time I was listening to the news, the school was calling to tell me . . . the student belonged to me. I was shocked."

Banks said that the boy was very active and well liked by his schoolmates.

Stunned neighbors were keeping their children close to home yesterday. Eugene Williams, who lives in the building next to the Arthurs', said, "I told my kids bikes are out. They're not going anywhere." He said he could not remember the last time a child from the neighborhood had been killed.

Steven Bennett, another neighbor, said he was surprised not to see Carl outside yesterday afternoon when another child was hit, but not injured, by a car. "Eric Carl was . . . very inquisitive. If anything happens, he's on the scene, but he wasn't out there yesterday," Bennett said.

Yesterday, Park Police said they did not know what the two 12-year-olds did between the time of the assault and 8 p.m., when they said one told a parent. Park Police searching the area later in the evening found Carl's bicycle near the path close to the water. It was missing a wheel.