THIS weekend I learned my toddler likes Gilbert and Sullivan. I had no idea. After all, we had never played the greatest hits from "H.M.S. Pinafore" or "Pirates of Penzance" around the house before. I only happened to discover this when we attended Arts in the Parks, a free Saturday morning entertainment program offered at four regional parks in Fairfax County.

Every Saturday morning at 10, Fairfax County serves up a varied assortment of family programs at four different locations -- Chantilly, Annandale, Reston and Burke. From Hawaiian dancing and symphony performances to puppetry arts, song and dance teams and, yes, even a Victorian lyric opera company, there is no telling what you're going to experience on a Saturday morning at the park. And, thanks to a sponsorship by area McDonald's restaurants, every performance is free.

Some of the themes of the performances promote awareness and responsibility for the environment, says Sousan Frankeberger, the events and volunteer coordinator for the parks. Other artists, such as dance troupes and symphony members, provide the more cultural portion of the program. The one thing all the performances have in common is the setting: all take place outdoors in park amphitheaters.

Although I had visited Lake Fairfax Park in Reston several times with my family, I had no idea there was an amphitheater on the grounds. Located away from the main attractions of the water park, carousel and lake, the amphitheater is nestled at the back of the park near the campsites. The stage and wooden benches are located at the bottom of the hill, under a overhang of trees. This picturesque and shady spot, only a short walk from the parking area, is a cool antidote to hot and hazy summer mornings. The wood benches are new this year, courtesy of a local Eagle Scout troop. If you're looking for comfortable plush chairs, be warned that seating is strictly utilitarian. But that does not seem to be a problem for most of the people here, since the programs are only an hour long.

Bob Brown, a puppeteer based in Arlington, is a veteran of television shows such as "Mr. Rogers' Neighborhood." He is a popular local performer throughout the area. He, like many other performers, will be appearing at all four park venues during the course of the summer.

Brown opened the first show of the season at Lake Fairfax in June. The crowd at this event was on the small side, about 50 adults and children. This number will grow as the summer wears on, with the average number of people at a performance reaching about 200.

Brown enjoys performing at the park's amphitheaters, citing the wooded setting and the intimacy of the space -- parents and children are able to come up to him afterward, to see the puppets and talk to him about the show -- although he will admit that it does have its challenges, specifically bugs, heat and weather. But even on the hottest days he can't see himself doing anything else, good-naturedly quoting the old punch line, "What? Leave show business?"

On the several weekends I attended performances, there were clear skies. If it rains, all events are rescheduled for Sunday, except at the Ellanor C. Lawrence amphitheater in Chantilly, where the show moves indoors to the Visitors Center.

One mother from Great Falls, when she saw I was taking notes, came up to me after the performance and asked me not to write about it, fearing the series would become "too popular." Her request was understandable. Since attending on opening day, I found myself returning twice with my toddler. On our last visit, we were treated to musical selections by Gilbert and Sullivan. Sitting outdoors, with the children listening to a song from "The Mikado," there was a feeling that the audience was sharing a well-kept secret. But not to worry, even if attendance grows there will still be plenty of room; most of the children weren't taking up any of the bench seats, they were too busy standing in the aisles, dancing.

ARTS IN THE PARKS -- Saturdays at 10 a.m. through Aug. 21 at the following locations:

Burke Lake Park Amphitheater -- 7315 Ox Rd., Fairfax Station. 703/323-6601. Take Beltway Exit 5 (Braddock Road) west to a left on Burke Lake Road and then another left on West Ox Road. Park entrance on left. Saturday, Bob Brown Puppets; July 24, Sue Trainor, singing and dancing; July 31, Outback Jack: animal songs from around the world; Aug. 7, Fairfax Symphony Overture: Strings; Aug. 14, The Bug Box, live exotic insect zoo; Aug. 21, Fairfax Symphony Overture: Percussion.

Ellanor C. Lawrence Park Amphitheater -- 5040 Walney Rd., Chantilly. 703/631-0013. Take Beltway Exit 9 to I-66 west 11 miles to Exit 53/Route 28. Turn left at the stoplight, drive 1/4-mile and make a right on Walney Road. The Visitor Center is one mile on the left. Saturday, Fairfax Symphony Overture: Strings; July 24, The Bug Box, live exotic insect zoo; July 31, Bob Martin, music from ragtime to rock 'n' roll; Aug. 7, HOALOHA, music of Hawaii; Aug. 14, Fairfax Symphony Overture: Woodwinds; Aug. 21, Victorian Lyric Opera: Gilbert and Sullivan selections.

Lake Fairfax Park Amphitheater -- 1400 Lake Fairfax Dr., Reston. 703/471-5414. Take Beltway Exit 10-B (Leesburg Pike, Route 7), drive west about 6.5 miles and turn left on Route 606 (Baron Cameron Avenue) and then make a left on Lake Fairfax Drive. Park entrance on left -- follow Arts in the Parks signs to amphitheater. Saturday, Sue Trainor, singing and dancing; July 24, Bob Martin, music from ragtime to rock 'n' roll music; July 31, The Bug Box, live exotic insect zoo; Aug. 7, Fairfax Symphony Overture: Percussion; Aug. 14, Fairfax Symphony Overture: Brass; Aug. 21, HOALOHA, music of Hawaii.

Mason District Park Amphitheater -- 6621 Columbia Pike, Annandale. 703/941-1730. Take Beltway Exit 6 (Little River Turnpike, Route 236) and drive east two miles and then make a left on John Marr Drive and a right on Columbia Pike to park entrance, just before Sleepy Hollow Road. Saturday, Fairfax Symphony Overture: Brass; July 24, Bob Brown Puppets; July 31, Bruce Hutton, American folk music with antique instruments; Aug. 7, The Bug Box, live exotic insect zoo; Aug. 14, HOALOHA, music of Hawaii; Aug. 21, Sue Trainor, music and dance.

CAPTION: Performers present music and dances of the Hawaiian Islands during an Arts in the Park program at Burke Lake amphitheater.