LAWRENCE — One hour before he died, 8-year-old Luis Rodriguez was playing, laughing and running around with friends at a birthday party.

"Parents are not supposed to bury their children. It isn't fair," the boy's grief stricken mother, Cynthia Crespo, said yesterday with her husband, Luis Rodriguez, at her side in a relative's home.

Their son died Sunday at Lawrence General Hospital after fainting at Imajine That, an interactive play space in Lawrence.

The cause of death was unknown yesterday, pending a report from the medical examiner's office.

The boy, who was a second-grader at Tarbox School, was scheduled to return to school Monday after being out three weeks with mononucleosis.

Crespo raised her head, and with tears streaming down her face, she smiled and said, "He was such a good boy."

She said her son had asthma and a peanut allergy, but that doctors at Lawrence General told her they believed neither was the cause of his death.

She said her son has fainted twice before — two years ago and last June — but that doctors did tests and "didn't find anything wrong with him."

Crespo, who is employed as a medical records coordinator at The Psychological Center in Lawrence, said her son had just recovered from a bout of strep throat and mononucleosis and had been cleared to return to school on Monday.

"I never, never, never imagined that this would happen," Crespo said.

"It's so difficult knowing he's not going to be with us," she said.

Crespo rode in the ambulance to the hospital with Luis.

"His heart was weak, but he was moving because he wiggled around trying to take the tubes off," Crespo said.

She said doctors performed CPR for a half-hour and will forever live with the nightmare of hearing them say, "We can't do anything more."

"I remember thinking, 'It can't be. It can't be,'" she said as she put her head down, wailing and nervously shaking her legs.

Luis has two sisters, Yareliz Rodriguez, 2, and Kearaliz Rodriguez, 4.

When Kearaliz asked her parents about him they told her he was with God.

"He's an angel watching over us," Crespo said she told her daughter, who then asked, "Is he with the birds? Am I going to see him up in heaven?"

Kearaliz later surprised her mother with a drawing she made for Luis. In it was a picture of her family, along with an angel with wings and a gate.

For now, Rodriguez, 30, and Crespo, 29, recalled the happy times with their son — watching the Red Sox in the World Series, playing ball with his dad at home and riding his scooter.

"He learned to ride a bike last year and he was so excited," Crespo said.

The parents, both natives of Puerto Rico who moved to Lawrence in the late 1980s, said Luis loved spending time with his grandparents, Cristobal and Yvette Rodriguez of Methuen. He loved to play with their Chihuahua named Max and enticing his grandfather to run after him, which always ended with a tickle on Luis' belly.

Although Cristobal Rodriguez has 12 other grandchildren, he said Luis was special.

On Monday, Tarbox School Principal Martha Duffy stood in front of Luis' classmates along with two counselors to tell them that their classmate was not returning.

"It was hard for them because they had just come back," Duffy said. "It's a hard age because they really don't understand."

"We're devastated. He was a very shy, but wonderful little boy who just went about doing his work," said Duffy, who also sent a letter home letting parents know about the tragedy. "He was very kind and conscious about his schoolwork."

He was a member of Cub Scout Troop 2 at St. Mary of the Assumption Parish.

Den leader Josue Maldonado said Luis enjoyed the many events with the Cub Scouts, including their trip to the New England Aquarium, touring a Lawrence firehouse and participating in the city's Hispanic Week.

Maldonado also remembered the excitement Luis felt as the Scouts went out looking for bugs for a science project.