PEOPLE KEEP asking Cathy Fink and Marcy Marxer what they want to be when they grow up. Or if they're ever going to grow up. It's certainly not because these national folk scene fixtures don't have the chops or the years in the biz. But singer-songwriter Fink, veteran of some 20 albums, and Marxer, an award-winning multi-instrumentalist, both Silver Spring residents who have been collaborating as a duo for a decade, have always split their performing time between grown-ups and kids.

Both camps of fans, big and little, come together Saturday when Fink & Marxer present their third annual Family Holiday Show at Montgomery Blair High School, featuring storyteller Len Cabral, and a free ice cream social donated by Ben & Jerry's.

Fink arrives to chat over morning coffee, but today Marxer is home sick with an occupational hazard -- a flu bug she picked up at one of the duo's kid concerts. But through the twin miracles of telephone technology and trick-editing, we can make this interview sound like a duet.

"People always come up and give you a big hug and then say 'God, I'm so sick.' Don't they?" Marxer laughs over the phone from home. "But we've gotten sick a lot less since we stopped playing elementary schools."

The two have spent their entire careers doing music for both kids and adults, says Fink. "And what you get out of each of them is very, very different. If I played 100 percent full time for kids, I probably wouldn't have written four songs about the {National AIDS Memorial} Quilt, or a song about a woman Vietnam veteran."

Says Marxer, "I kinda can't imagine playing to just one kind of audience. I mean, it's like saying 'I'm only gonna relate to people from one specific age group and skin color with this political leaning.' That just goes against what folk music is about."

Grown-ups and kids, Fink and Marxer agree, expect and appreciate entirely different things from performers.

"Adults really appreciate your harmony sound, your instrumental virtuosity, technical stuff. They can get into something long and deep," Fink says.

"Kids, they're really interested in what they're doing -- it's like being a musical activity leader," Marxer adds. "People come up to us and say 'God, when do you breathe, before the show or after the show?' Because you can't have a minute of silence while you tune your guitar. A minute of silence goes by and you've lost them."

Marxer says they don't really act a different way at different concerts. "We're exactly the same people, except for at the kids' shows we wear dorky matching outfits {which their mothers found for them}. It's great for the shows, but it's kind of weird when you go out for lunch afterwards."

So, at both the duo's grown-up and kids' shows, you're likely to hear lots of strong songs and sweet singing with guitar/banjo/fiddle/mandolin accompaniment, a bit of speed-yodeling and slap-cheek playing, and maybe a demonstration of homemade instruments like washtub bass and oatmeal box banjo. And if you're lucky, Marxer will demonstrate her latest passion, cowgirl rope tricks. But only kids get neato stuff like the giant purple papier-mache sneaker Fink & Marxer lavished a week on building for one of their tunes.

An accordion, of all things, brought the duo together. Fink was performing solo and Marxer was playing in a four-piece all-female band called the Bosom Buddies String Band, when the two acts were simultaneously booked at a Canadian folk festival.

"I thought accordion was just the wimpiest instrument in the world," Fink says. "But when Marcy came out and started playing this button accordion and singing this incredible song called 'The Airship Song,' I knew I had to have an accordion, and it had to look exactly like hers . . . . So I immediately ran out and bought the button accordion of my dreams, and we started clearing out parties with accordion duets. The only thing worse than one accordion is two."

"What really happened was that we started doing more and more shows together," Fink says. "I would be booked for a Cathy Fink show, and I would bring Marcy along to play guitar or mandolin or sing harmony. It took us quite a while to wake up to the fact that what we were really doing was playing as a duo."

Along with last year's radiant self-titled "grown-up" album, Fink & Marxer have three kid albums, with a fourth due next year. This is classic stuff, enduring after many go-rounds, not something that's quickly outgrown. Fink's "When the Rain Comes Down" and "Grandma Slid Down the Mountain" and Marxer's "Jump Children" are reaching their third generation of kids. And "Help Yourself," their most recent album and second as a duo, is built around a constructive theme, a playful pop pep talk centered around self-reliance and self-empowerment for kids. The pair have also made two well-received videos, "Making and Playing Homemade Instruments" and "Kids Guitar."

"What we do has a really broad appeal age range," Fink says. "It doesn't stop in the first grade. It goes all the way through fourth or fifth grade. And that's a pretty long time to be able to hang on to a fan, from the age of 2 to the age of 10. Even in pop music, fans don't hang in there for eight years, unless it's a cult thing. I mean, Bob Dylan's fans from 20 years ago are still there, but three years from now, everybody will have forgotten New Kids on the Block, we can hope. Can't we?"

CATHY FINK & MARCY MARXER -- Appearing with storyteller Len Cabral in a holiday family concert Saturday at 11 at Montgomery Blair High School, 313 Wayne Ave., Silver Spring. Contribution of a new toy for a needy child is suggested. Call 301/270-9090.