It was a hot day near noon yesterday, and 5-year-old Joshua Tyler Deen just wanted something cold to drink. His mother, Helen, stopped at a grocery store in Silver Spring, blocks from their home. Joshua was just steps ahead of his mother near the store entrance when a car suddenly careered toward them from the parking lot.

Rohena Nelson's 1991 burgundy Oldsmobile Cutlass hit the child straight on, slamming his head against the hood and pinning his body against the concrete-block wall, according to Montgomery County police and witnesses.

Within seconds, a group of sanitation workers on lunch break nearby pushed the car away from the wall and a Giant employee began cardiopulmonary resuscitation.

"My son, my son, my son!" Helen Deen screamed as Joshua lay unconscious and bleeding.

The boy was in cardiac arrest, police said, and by the time ambulance workers got him to Washington Adventist Hospital, Joshua was dead.

"His mother was hysterical," said David Robinson, a Giant produce clerk and an emergency medical technician for the D.C. fire department who tried to help the boy. "She kept yelling, 'Do we have a pulse? Do we have a pulse?' But my job was to do CPR. We worked until the medics came."

At the hospital, members of the Deen family gathered, praying and sobbing in each other's arms. At one point, a number of them met with hospital chaplains behind drawn blue curtains in the glass emergency room cubicle where the boy's body lay.

Helen Deen's only child had just finished kindergarten and had proudly displayed his diploma. He was 10 days shy of turning 6.

"He was such a bright child. And so very loved," said one family member. "Just last night was his grandfather's birthday. We were all together, and Joshua said, 'I get to cut the cake!' "

Police are still unclear how Nelson, 64, who lives on Valleyview Avenue in Takoma Park, lost control of the car. By late yesterday evening, she was still being held for observation at Washington Adventist.

Robinson and other witnesses at the Giant on Arliss Avenue said they saw Nelson's car heading toward the front of the store with the left-side door open and her leg dragging along the ground.

"We heard the engine running real loud, like she was accelerating, and then saw the car streaking across the parking lot," said Anson Jackson, a sanitation worker who was lunching on a bench in front of the Giant. "At first I thought some wild, crazy person was going to ram the store."

"It looked like she didn't have any brakes," Mauricio Benitas, another witness, said through a translator. "It looked like she didn't even try to stop."

The force of the impact against the concrete wall broke the front bumper off Nelson's car, crumpling the hood and hurling blocks of debris into the store.

"We have no idea why she accelerated or how fast she was going," said Montgomery police spokesman Derek Baliles, but it was "a pretty good rate of speed." No charges have been filed, he said.

Witnesses said Nelson's car was traveling fast--one estimated between 30 and 40 mph. "She was in shock, bleeding," said Walter Doyle, another sanitation worker.

Officers from the collision reconstruction unit are investigating the cause of the crash. Gloria McCloud, an acquaintance who answered the door at Nelson's home, said Nelson had undergone major head surgery in the last year.

As Doyle, Jackson and others rushed to free the child, they yelled at Nelson to take her foot off the brake or put the car in neutral. Then they rolled the car back.

At the same time, Robinson and other Giant employees, including the pharmacist, began tearing away the damaged brick wall to get to the child. Once the car was pushed away, they laid Joshua down on the ground and began CPR.

Washington Adventist spokesman Robert Jepson said Helen J. Deen, 28, of the 8500 block of Tahona Drive in Silver Spring, works in the admitting department, not far from the emergency ward where her son was taken. Other relatives work in the hospital's labs and in the radiology department.

"There are about five family members of the boy who work here," Jepson said, as he stood outside the emergency room. "So the news is rippling through the hospital, and people are just devastated."

Stunned relatives and co-workers gathered in the parking lot, and one employee struck his forehead with the palm of his hand in disbelief as another worker told him what had happened.

Said Baliles: "It's awful."

Staff writer Manuel Perez-Rivas contributed to this report.

CAPTION: A sanitation worker for WSSC was among those who gave CPR to the Silver Spring boy, who died soon after.

CAPTION: Officials investigate the scene where a 5-year-old boy was killed when he was hit by a car in the parking lot of a Giant supermarket at Flower Avenue and Arliss Street in Silver Spring.