Donna is biting Kelly: a 4-year-old making trouble and a 6-year-old resisting only enough to make the game more fun. As Kelly squirms away from the pink mouth and tiny teeth, Donna lunges in her sister's direction, her hands flapping around Kelly's small head where the hair that fell out during the radiation therapy is just beginning to grow again.

When the giggles have subsided, when first-grader Kelly Moorleghen is no longer nervous about the strangers who have come to talk to her and take her picture, she explains she is hoping to get a Cabbage Patch Preemie soon, "because my sister was a preemie." She already has three Cabbage Patch Kids in addition to a collection her mother Debra estimates includes 200 other stuffed dolls and animals that were sewn by friends, given by employers, sent by strangers, friends, celebrities and parents of children who, like Kelly, had cancer, but unlike Kelly are no longer around to play with their dolls.

Kelly has leukemia. Donna, born three months premature, is multiply handicapped. She cannot stand, cannot sit on her own, can get out only a few words, is not blind but sometimes seems it. Diane, Donna's twin sister, died when she was 18 hours old. Paul and Debra Moorleghen, who didn't even know they were going to have twins, had to decide to take Diane off the respirator. Thirty minutes later she was dead. One year later, Kelly's leukemia was diagnosed.

"I always thought, 'Whatever happens to Donna, we've got Kelly. My first child,' " says Debra. "Right now, it's really: Five years down the road, will we have any kids?"

Two months ago, the Moorleghen family went to Disney World, sent to Florida by the Make-a-Wish Foundation, a national volunteer organization that grants the wishes of terminally ill children. Except for one day at the beach, it was their first vacation since Donna's birth four years ago.

"It was a vacation away from the hospital," says Debra, 28, a budget analyst for the Navy Recruiting Command. "As Kelly said, 'Good, we won't be around the hospital this week.' Kelly is treated at NIH and Donna at Children's. Work is very supportive. When Kelly has a down period, or Donna, then I'm off work. All the time I'm off, it's usually at the hospital."

But for those four days, they really had a vacation. The Moorleghens were flown down to Florida, met by a limousine that had once carried Michael Jackson, put up in a nice hotel, introduced to Mickey Mouse and Pluto and a killer whale. Kelly sat on the whale's back, which she says was "gooey, slimy and mushy," and used the spending money the foundation gave her for a whole new supply of stuffed animals. She held her sister on her lap and went on ride after ride after ride, and one night, standing on a restaurant's balcony and looking down into the water, she spotted an alligator.

"Financially, we probably didn't need someone to pay for it," says Kelly's father Paul, 38, a transportation specialist for the Department of the Navy, "but what the trip really did -- it forced us to do it."

Make-a-Wish, one of several similar organizations around the country, was founded in Phoenix a few years ago. The Washington branch opened in 1983 and has granted 19 wishes so far.

Thousands of children suffer from cancer in this country. According to estimated figures collected by the National Cancer Institute Surveillance, Epidemiology and End Result Program and published by the American Cancer Society, 1,100 children under 15 died of leukemia in 1978, the last year for which such figures are available. That year, 2,550 children under 15 died from all cancers. There were 1,875 new cases of leukemia diagnosed in 1978 in that age group, and 6,100 new cases of all cancers.

"There's actually very little done for these children," said Make-a-Wish Washington branch president Jane Martens recently. "Once everything that can be done medically is, people tend to back off because it's so difficult to deal with the fact that this child will die. People can't deal with the pain. A lot of these kids haven't experienced anything but discomfort and anxiety for years. But with Make-a-Wish, somebody's doing something. They're not just backing off. They're hugging them."

The pictures from Florida are spread out in front of Kelly: Kelly on the whale, Kelly and Donna and Debra laughing, elephants spouting water, a huge Pluto licking the face of a small, less than thrilled Kelly. A pale girl in white tights and a red dress that matches her sister's, Kelly looks at the pictures and says her favorite things about the vacation were the whale (despite the gooeyness), the roller coaster, and the pizza she ate at every chance.

"ROOM SERVICE!" Kelly bellows, imitating the announcement heralding the nightly pizza. "One night, she sneaked mints under our pillows."

"They had flowers in the room, they pulled down the sheets," says Paul.

"The works," says Debra.

"I took them all out and ate them all," says Kelly.

Kelly's NIH social worker describes the Moorleghen family as "strong," and Debra and Paul use the same word when they speak of their daughters.

Their house, despite the wheelchair in the corner, is no different from other cozy, plant-filled Arlington homes. A brightly painted wooden doll hangs from the door knocker, a plump Christmas tree twinkles and waits in the den. The talk is often of "chemo" and Kelly's decision recently to stay at the hospital without either of her parents spending the night, how she pushed her own IV pole through the halls of NIH, how one mother wouldn't let her daughter play with Kelly because she was afraid leukemia was contagious. But it is also of Cabbage Patch Kids and day care and how many digits a telephone number has and the pink slippers with flowers Kelly will give Donna on Christmas day.

"Who's this for?" Kelly asks, all innocence as she hands a visitor a package from under the tree. She smiles conspiratorially when the name "Kelly" is read.

"I think sometimes she's so spoiled," says Debra, "but then I think that she has the right to be. She may only have a year to be spoiled. Someone else will have their whole life."

Part of what Kelly's getting is a life as close to normal as her parents can manage.

"They want you to try to keep the child's routine as normal as possible," says Paul. Kelly is wrapping Donna in an orange chiffon scarf, pulling it tight around her sister's head as her mother, a thin blond woman who smiles often, distractedly tells her to be careful. "We try to keep it normal. She's got to respect her parents too."

And so things move along. Both Donna and Kelly go to school -- Donna to a special program in the Arlington school system, Kelly to a private school. Paul and Debra work full time.

"I was talking to my boss at work, and he said, 'You know, I really admire you,' " says Debra. "I don't know how you raise a family, go to work, fit in your hospital visits.' Several people have asked, 'Why do you keep going to work?' I think if I was here with her all the time, I think I'd begin to feel sorry for her, for myself, and that wouldn't help any of us. I think I'm a better person. It's my out and her out."

Kelly wanders off, then reappears for a second.

"Don't worry, Momma, I took my pills," she says, and returns to the television.

Debra's parents live an hour away, Paul's down the street. Between them they have more than a dozen brothers and sisters, and they help too.

"The neighbors -- they know when my car's gone for two days, Kelly's back in," says Debra. "There'll be gifts out on the porch for her."

The Moorleghens want to talk about Kelly and Donna, they say, partly to thank all the people who have helped them, from the people at radio station WPGC to the Washington Redskins, and partly to reach other parents like themselves.

"It's scary out there. I never realized kids have cancer the way they do," Debra says. "We'd never been exposed to it. If you don't tell people about it, and what it's like, as far as I'm concerned, they're going to come out to the same scary place as we did. The best thing to do is you don't try to hide what's going to happen, the heartache that's going to be there."

For example, when Kelly started to lose her hair the first time, people stared at her, the kids at public school called her "baldy."

"People aren't used to seeing a bald child," her father says. "She looked like a little Martian."

She soon learned to glare back.

"That's why I think it's an important thing for people to know these kids are out there," says Debra. "They're not hidden anymore."

"They're kids before anything," says Paul. "They're still kids."

NIH social worker Andy Tartler has worked with the Moorleghen family for more than two years, consulting with them and their doctors, explaining things to Kelly, bringing clowns and balloons to distract her during radiation therapy.

"This family definitely is an unusually supportive, warm group of people," he said recently. "They have the strength as a family to accept help. Kelly's been through the mill. Pediatric cancer treatment can be extraordinarily disruptive to normal family life."

The mill for Kelly has consisted of lung surgery, chemotherapy, shingles and the spinal and cranial irradiation that, as her father says, is the treatment of last resort.

"I'd say we're down to 30 percent," says Paul of Kelly's chances for survival. He is a calm man who speaks quietly and smiles as he talks, even when he says this. "We don't really talk about that. We talk about getting better. The whole thing is to get better.

"We're not really expecting to lose her, but you know it's definitely a possibility. It might even be a likelihood. But those kinds of things -- I block them out until I'm forced to deal with them."

The children are asleep now, snuggled together upstairs in the double bed they share. The house is quiet.

"I know things could get worse," Paul says, attempting to explain his equanimity.

His wife looks at him, grimacing and smiling at the same time, shaking her head.

"They could?" she asks, and they both laugh.

"Worrying doesn't get you anywhere," Paul says. It's his motto.

When Donna was born, they joined a support group for parents with handicapped children. "Commiseration sessions," Paul called them.

"I thought the whole thing was a pain in the tail, myself," he says. "Debbie got so much more out of it."

"It makes you feel you're not alone," she says.

"Misery loves company," he mutters, laughing.

Their styles are different, but in the end, they share the same sense of fatalism.

"We don't keep asking the 'Why? Why?' questions," Paul says, his voice full of mock melodrama.

"Whenever I get down I call Mom -- she's very supportive," Debra says. "She'll always say, 'God gave them to whoever he thought could handle it. If he didn't think you could handle it he wouldn't have given them to you.' "

They can handle it -- the months on end without a night spent out of the house, the deaths of Kelly's friends at NIH, the mood swings chemotherapy brings. They can handle the day-to-day, but there are some things that even they cannot handle, like having another child.

"We've thought about it," says Debra, "but I don't think I want it. I think we've given it a good shot."

She is silent for a moment. "The big fear is having one, and watching it pass Donna. I don't think I could bear that."

Now, their two daughters are doing all right. Donna can move an arm doctors never thought she would. Kelly is in school, not feeling too bad. She likes the Cherrydale Christian School she attends, where every day the 10 children in her class pray that Kelly and her sister will get well. The Moorleghens were both raised as Catholics, but Kelly hadn't been exposed much to religion before she went to this school, where her parents sent her because they felt she was getting lost in the large public school classes.

"When they pray every day, she asks them to pray for Donna, not herself," says Debra. "They ask God to make her better. I think that's touched her."

"I think she blocks out her own prospects of dying," Paul says. "But she sees co-patients do well, slide down, come back and eventually pass on."

"I think she thought only the older kids could die at first, that this couldn't happen to her, she'd be fixed before," says Debra.

But recently, a girl her own age with whom she had roomed at the hospital died and now Kelly talks to her mother about heaven, where, she says, the angels feed each other with their wings because they have no hands and everything is beautiful and everyone loves each other.

"What?" Paul asks in disbelief, as Debra describes this.

"I don't know if she saw it on a program or what," Debra says. "That's what she's telling me."

"I think that's why she likes her school," Paul says. "It gives her something to . . ."

Debra completes the thought: "to hold on to."

Paul: "You roll with the punches. When she was first diagnosed -- my experience with leukemia was, I was going to lose her. But I'm thankful for what I've gotten so far."

"I think that's just what we wanted at the beginning," says Debra. "Just give us time, if nothing else. Give us time, give her time to enjoy her life. It could have been over 2 1/2 years ago, and it wasn't.

"Each time we'd come to a rough spot, I'd think, 'We're not going to get through it,' but we did."

She shrugs her shoulders, and she smiles.