AT HAINS POINT on a frigid Sunday morning, several dozen runners in bright woolens and sweatsuits limbered up for the D.C. Road Runners' weekly two-mile race. Some jogged in place or across the frozen ground. Others struck calisthenic poses under the bare trees.

A few, limber enough to skip the rituals, spent their time sliding on ice patches.

These were the children - 10 year-old Brian Sharager of Rockville, Timmy Robertson, 8, of Oxon Hill and John Broderick of Upper Marlboro . . .

Lately, youngsters across the country have begun to jog, "run-for-fun," and enter amateur events - from dashes to marathons - while most others their age are just running to get from one place to the next.

What happens when this child's play becomes sport? Must companionship turn into competition? What goals have these runners and their parents and coaches set?

Fifteen years ago nobody asked such questions. According to Runner's World, "nobody ran until high school." Then the AAU begun pushing its Junior Olympics and preschoolers began marking headlines.

In 1968, 5-year-old Mary Etta Boitano crossed the finish line before any other female in the Dipsea cross-country in California. She now holds the AAU-certificate marathon records for U.S. females ages 6 through 10. In 1971, 3-year-old Kevin Strain of Juneau, Alaska, ran an age-group record mile in 9:52. The following year Steven Parsons of Northfield, Ill., covered a mile in 24:16.6, a record for his peers - birth to one year.

Today sports annals list records for one-year-olds and up for every event from the 50-yard dash through the three-mile race.

There's a strong body of opinion, however, that long-distance running should be preferred over dashes for children.

"Any event that's particularly stressful - like sprinting 25, 50, 100 meters - isn't such a good idea," said Rory Donaldson, program adviser for the National Jogging Association, whose 13-year-old son Chris has been running since age 10.

"That's taking an undeveloped muscular-skeletal system and pushing it through short distances, and I don't see any particualar reason to do that.

"I think it was Tom Bassler, an M.D. in California, who said that running is okay for kids as long as the finish line is in the next county. The long race. The longer, probably, the better.

"Definitely, that way the child as well as the adult is going to get the kind of training we're interested in - endurance, cardiovascular training."

Beyond the immediate and obvious however, no one can safely say what effects sprinting or long-distance running may have on children or adults.

That is why last October 400 doctors met in New York City for a conference title "The Marathon: Physiological, Medical, Epidemiological, and Psychological Studies." Explored were topics like metabolism is prolonged exercise; body temperature and fluid balance; cardiovascular function and limitations during prolonged exercise; and pathological effects of long-distance running.

Pros and cons, nontheless, continue to pile up.

Those who oppose the idea of children running point to injuries, interference with normal growth, emotional effects of high-pressure competition and time-robbed from regular play.

Proponents contend that children already play the way long-distance runners train, that risk situations can be curbed by school administrators, coaches, and parents, and that, although children are naturally competitive, competition doesn't have to be high-pressure.

"Whether you want your children to run or not," said Donaldson, "they do run. Because that's what they do. They get up in the morning, start running, and then a little later they go to bed."

Egan Kafka, head of the Federal Interagency Jogging Council, has been running since he was a boy in Switzerland. "At age 9 or 10," he recalled, "we would run two, three miles, on the road, on the track. But when I came to this country in 1938, I found that track was deemphasized until the last two years of high school. I think that it's good for the younger ones to get out there as long as the pressures parents put on the kids don't go too far."

Donaldson agreed. "Comperatively speaking I think that children should run, but that parents should stay out of it," he said.

"I have seen kids feel crumby because they weren't doing as well as their parents thought they would, and I've seen kids dragged through a marathon because their parents wanted them to complete it.

"But if the kids wants to get out there, seems to be doing well and is growing straight of limb, and it the parent isn't browbeating the child, then competition is fine."

There are those who say coaches should stay out of it. Jean Rowe of Gaithersburg said that although her nine children, ranging from 12 to 25, have made many track records and won many prizes, she never thought they should train seriously too early.

"To say 'seriously' at that age," she said, referring to her youngest - Hannah, 13, and Eddie, 12 - "would be against everything in our philosophy. We run as a family, because it's something we like to do."

"There are people in the area, however, who are very, very caught up in the age-group thing, and who believe that the track star of the future has to start as a very young child and be trained."

Rowe favors the D.C. Road Runners' family-pace style of competition. She told the story of the time Hannah ran her first 14-mile race with them.

"It was in Alexandria a few years ago, and Hannah was still in sneakers. We hadn't yet bought her running shoes; we didn't think we should or had to. And her legs started to hurt, and a man in the race stopped, rubbed her legs, helped her, and ran with her for the rest of the race. This man is a very good runner and probably could have achieved something for himself that day. But he helped her instead."

Then there are those who leave it up to their kids.

Jeannie Forehand of Rockville has two children - Vriginia, 14 and John, 12 - who entered a 50-miler in November 1975, and have been competing ever since. "I know it looks like we pressure our kids," she said. "We'll take them anywhere to train or race at the drop of a hat. Last winter I sat in the car in the dark every night while Virginia ran her five miles at the junior high. But it's not pressure, it's cooperation.

"A lot of people have suggested that these kids shouldn't run so much. But they know when they're tired out. They know when to stop."

Parents and coaches also differ on goals of competition.

"Everybody jogs," said Forehand, "but it's really fun to win. I will donate a trophy any day for the youngest runner in the race. I think that it's important for them to get something, even just simple ribbons.

Simple ribbobs don't satisfy all young runners, such as those who recently gathered at the University of Maryland to compete in indoor track events.

These were 8, 9 and 10-year-old world record-holders, national and state champions from the Model Cities Track Foundation, CYO Track Club and others. And as Charles Ryan, Maryland Track and Field Development Association chairman sees it, "Although Olympic potential isn't developed until the college level, the people who eventually succeed at international competition don't just show up every four years. They've been running for a very long time."

The Reston Runners don't plan that far in advance. A group of 40-60 children from 6 up, they have a decidedly low-key approach. As leader Joe Flagg says, "The children hopefully get the idea that sports, to be enjoyed, need not be competitive."

One thing is certain: it is the adults who are pondering the troubling questions of training for children. The children just run.

"It's fun," said 8-year-old John Broderick.

"I like to keep in shape," said 10-year-old Brian Shrager. "It's like a habit," said Hannah Rowe, who holds the U.S. 10-mile record for 12-year-olds: 66:13.

"My sister got me started," Hannah said. "I used to run with her until she went to college. I like long distances best. I go two miles after school, six miles after supper with a guy in the neighborhood who's on the high school team. The races are easy, training's the hard part.

"But last year I saw the Marine Marathon through the streets of Washington and I thought, hey, that looks like fun. I wanted to be out there. So that's why I'm preparing.