The children started leaving their homes before 9 a.m., many of them locking their front doors with keys that dangle from their necks the rest of the day. Scores of youngsters wound through the parking lots of the modest apartment complexes that surround Rogers Heights Elementary School.

It looked as though a typical school day was about to start, only this is the middle of summer.

Rogers Heights in Bladensburg is the home of one of the hundreds of summer playground programs that provide inexpensive recreation and activities to more than 48,000 elementary school-age children in the District, Alexandria, Prince George's, Montgomery and Fairfax counties, and hundreds more in other area jurisdictions.

More important, though, the playgrounds provide adult supervision in communities where many children are otherwise left to amuse themselves while parents work. The parents have found the playgrounds a free or low-cost solution to their day-care needs, generating concern among recreation authorities who say the playgrounds are not designed or equipped for it.

The Rogers Heights playground program operated out of the school lunchroom from 9 a.m. to 3 p.m. But "a lot of the little ones are banging on the door at 8:15," said head counselor June Felix, "probably because their parents have gone to work."

The playground programs, which are free in most jurisdictions, offer traditional day-camp activities: relay races, water balloon fights, crafts and field trips. But the programs are loosely structured: Attendance is on a walk-in basis; children are free to come and go during the day; and often there are only three to five counselors for groups that sometimes swell to include 90 children.

"It is not intended for day care. It is summer recreation . . . . Period," said Deborah Deutsch, of Fairfax County's Department of Recreation and Community Services.

Area recreation departments also operate traditional day camps, which cost from $50 to $150 for a two-week session, plus additional fees for extended hours care. Recreation authorities, who said they have had no serious incidents at the playgrounds this summer, said the day camps are better suited for child care because of their longer hours, larger staffs and closer supervision of children.

Sonia Haley, an insurance claims adjuster, sent her daughter, Renada Parrott, 9, and niece, Charmaine Parrott, 11, to Rogers Heights while she was at work. The playground provided for free similar activities as a nearby day camp that would have cost her $160 every two weeks for the two girls, she said.

"The playground has really helped us out a lot," Haley said. "At least {the girls} don't have to sit in the house all day . . . . "

The Maryland-National Capital Park and Planning Commission operates 124 playground programs in schools and recreation centers in Prince George's County. About 22,000 county youngsters have attended the programs this summer, nearly twice the number of children in the county-run day camps. At least 109 children have attended the Rogers Heights playground this summer, most of them from the modest mid-rise and garden apartment complexes just off Annapolis Road.

The Prince George's playground programs end today and counselors are concerned about how many of the children will spend the rest of their summer days.

"A lot of them will having nothing to do," said Felix.

Home base for the children who spent their days at Rogers Heights is a room that serves both as a lunchroom and an auditorium during the school year.

Here they started their mornings with board games, such as "Trouble" and "Connect 4," and arts and crafts. Last week they made cardboard robots and painted yo-yos in neon colors.

There were also Friday ice cream parties, soccer and kickball games, swimming at nearby pools and, this week, a trip to Wild World amusement park.

But many children still wandered about the schoolgrounds on their own, joining in hand-clapping games, playing in a sand pile or going to a nearby corner store for candy and soft drinks.

Counselor Keith Moore, a University of Maryland senior, tried to keep the children from leaving between activities by the host of impromptu game shows, talent shows and pop quizzes.

"What's two times five minus two plus one?" Moore asked over a microphone last week.

"Nine!" screamed a 9-year-old girl.

"Correctamundo!" Moore exclaimed, using the lingo of the popular Teenage Mutant Ninja Turtles.

"We try to cover a lot of bases in one day with a lot of activities," Moore explained later. "We give 'em . . . some surprises and most of the time they don't leave."

One afternoon recently, after bidding Moore and Felix goodbye, the children scattered to their respective apartment complexes.

Some remained outside to play in the parking lots. Alfreda "Nicky" Nieves, 11, said she lets herself into her aunt's apartment and awaits her return around 5 p.m.

Back at home, playground regular Prentiss Emmons, 12, sat with his friends on the steps outside the Mattapony Apartments.

"We don't want to be on the streets or get involved with drugs," said Prentiss, as he and his friends contemplated how they will spend the rest of the summer.

"We'll just hang around. Talk. Watch TV," said Rodney McQueen, 12. "Or {play} Nintendo."