OKLAHOMA CITY (AP) — P.J. Allen starts to wheeze, sucking air through a tube in his throat as he crouches on the floor and calls his dog.

The 7-year-old bounds off to find saline solution and give himself a "breathing treatment."

P.J., one of six children who survived the Oklahoma City bombing, inhaled hot air during the explosion that seared his lungs. His skin is scarred from burns and flying debris, and he has two bald spots on his head where pieces of rubble lodged in his skull.

Still, he is one of the lucky ones. The April 19, 1995, blast at the Alfred P. Murrah Federal Building killed 168 people, including 19 children — most of them in a day-care center on the second floor.

Six years later, most of the surviving youngsters have outgrown the nightmares. But the scars, mental and physical, remain. And P.J. and his five former day-care playmates have only begun to comprehend what happened.

"I was hurt in the bombing and I have to have this to breathe," P.J. tells other children who stare at his tracheotomy. But P.J. cannot explain the bombing itself.

"When we had the May 1999 tornado he saw it on TV and thought he had finally understood what happened to him," said Deloris Watson, his grandmother. "I think it's easier for him to comprehend a force of nature than a deliberate act by an individual."

P.J., a happy, rambunctious boy, plays basketball at the YMCA. He spends weekdays with a teacher at home because regular school would expose his damaged lungs to too many infections, his grandmother said.

Doctors believe P.J.'s lungs will be strong enough that they can remove the tracheotomy tube when he is 11.

Tears welled up in the eyes of Christopher Nguyen, another of the six child survivors, when his father took him to a fourth-anniversary ceremony at the bombing site. Christopher was 9 then.

The boy stared at a photograph of bombing victims Chase and Colton Smith, which hung on a chain-link fence surrounding the field where the federal building used to stand. He knew them from the day-care center.

"If they didn't die they'd be my age, right Dad?" he asked.

Thu Nguyen asked his son if he knew why they died. "The bad guy did this," the boy said. He didn't know the bad guy's name.

Christopher, now 11, and his father have not discussed it since.

"In his young mind and heart, I think he forgives," Thu Nguyen said. "I think he forgives those haters."

The blast hurled Christopher into a metal bar in a bathroom. His jaw bone was misaligned, he suffered head injuries and he had internal bruises throughout his body. His face was wrapped in gauze for weeks, only his eyes visible.

For two years, Christopher slept in a bed next to his parents so they could comfort him when he woke up crying. The nightmares stopped after a year and a half of therapy.

Thu Nguyen still does not understand how anyone survived the blast, let alone why his son was one of the lucky ones.

"Every day we are grateful," he said. "It's just really something of a miracle and we couldn't explain that. Nobody can."

Jim Denny tells his children they are two miracles. "There's not any rhyme or reason for why they survived that. God has a special place for them," he said.

Denny said having Brandon and Rebecca survive was "like winning the lottery five days in a row."

The scars on 8-year-old Rebecca's face are fading. The redhead spent 10 days in the hospital after rescue workers pulled her from the rubble.

Brandon, now 9, had severe brain injuries and spent months in the hospital. The boy still goes to occupational, physical and speech therapy every week. His right hand doesn't grip and he walks with an uneven gait.

"Whatever questions they ask we answer honestly," Denny said. "We've tried to explain terrorism to them. We try to explain to them there are very few evil people in the world and Timothy McVeigh is one of them. We concentrate on the good people and what we can do to help them."

Joseph Webber, the youngest survivor at 19 months, has overcome his injuries 99.9 percent, said his father, U.S. Attorney Dan Webber. The blast broke the toddler's arm and his jaw, burst his eardrums and knocked him unconscious.

"He knows that he was in a building that was blown up and he knows that it was done by an intentional bombing," Webber said. "We've avoided telling him a lot of details to avoid having him look at life with fear."

At 4, Nekia McCloud spent five weeks in a coma and twice nearly died. She had to start life again from the baby stage. The bombing damaged her brain, forcing her to learn again how to walk and talk. Now 10, she does not remember any of it.

Kia, as she is called, has recovered remarkably and does well in third-grade despite memory problems, said her mother, LaVerne McCloud. She spends afternoons playing with friends, adding bicycle accident scars to the ones the bombing left on her arms and legs.

The McClouds do not talk about the bombing. They do not attend anniversary ceremonies and do not plan to watch McVeigh's execution May 16.

"We try to get on with our lives," LaVerne McCloud said. "How are you going to forget if they keep bringing it up?"