A sharp-looking threesome -- son, father and grandfather, perhaps? -- saunters across the lobby of the Key Bridge Marriott. The kid is gulping down a bottle of orange soda, the father wiping the sleep from his eyes. But the grandfather, resplendent in an oversized red sweater, looks eager, alert, ready for action.

They're not, in fact, relatives, but after spending the past seven months starring together in the national touring company of ''The Tap Dance Kid,'' dancers Dule Hill, 10, Eugene Fleming, 24, and Harold Nicholas, 60, have come to constitute something of a family. In the show, which opens tonight at the Warner Theatre, Fleming plays Hill's uncle and Nicholas his grandfather. But the artistic family ties extend beyond this fictional context -- directly down to the feet. The art of tap dancing binds these three together.

And once the rhythms get laid down and the hoofing heats up, any vestige of a generation gap dissolves.

''I was never drawn to any dancer as a role model -- that is, until I saw Harold,'' says Feming, beaming at Nicholas. ''I didn't get to see most of his work until I was 21, and that's a real shame, but I think Dule has the greatest opportunity he could ever have to work with Harold and to see his stuff.''

The ''stuff'' to which Fleming refers is the collection of acrobatic dance routines created and performed by the Nicholas Brothers -- Harold and his older brother Fayard -- in such 1940s movie musicals as ''The Pirate,'' ''Stormy Weather,'' ''Sun Valey Serenade'' and ''Down Argentine Way.'' Though the brothers also appeared in vaudeville and on the stage of the Cotton Club, it is the film work -- compendium of some of the smoothest slides, splits, leaps and steps imaginable -- that afforded them far more recognition than most other great black dancers of that era, as well as a tangible legacy.

''Back then, we were the only ones who actually had a contract with a studio,'' remembers Nicholas. ''But still, in the movies we made, all we did was dance. That's the difference between us and Kelly or Astaire. They did everything -- they acted, they sang, they got the girl. Stories were written for them, but they put us in a story. Yet I think we went as high as any black dancers could go.''

Ironically, the smiling, stylized, carefree image perfected by the Nicholas Brothers and their tapping confreres lost favor with a lot of blacks during the '60s and '70s.

'' 'The Tap Dance Kid' has a lot to say about how many black parents were trying to get away from dancing, because they felt it was sterotypical, Uncle Tom-ish,'' explains Fleming.

''I think there are more whites wanting to tap-dance now than blacks,'' says Nicholas, who spent 11 years living and performing in Paris when his livelihood dried up in this country. ''Believe me, I ask myself why that is. Maybe black people don't think its dignified enough. It's very sad. Take the father in this show. He feels that his son isn't going to make anything of himself by dancing, and he's wrong.''

Fleming's understanding of that father-son relationship stems from his own struggle to validate his career choice.

''I took my first tap lessons when I was about 4 or 5 in Richmond, where I grew up, and started ballet at 12. I went through all the phases -- the guys calling me 'Twinkle Toes' and stuff -- But I enjoyed dancing so much that I just kept doing it,'' he says. ''My mother was totally into it, buy my father kind of wondered.

''One day he said to me: 'You think that dancing will ever make you any money? Man, why don't you get a real job? After all, he was paying for all my lessons. But dancing was the only thing that I was really good at. I wasn't any good at nailing nails. And when my father is a barber -- I cut this hole in a guy's hair. I think that was it for barbering.''

Fleming's perseverance eventually paid off. After studing at the North Carolina School of the Arts on a ballet scholarship, he was cast in the national company of ''A Chorus Line'' and -- along with Nicholas -- in two West Coast productions of ''Sophisticated Ladies.'' These professional gigs helped to convince his father that dancing is indeed a legitimate occupation, so much so that Fleming's current bio states that he ''dedicates this performance [in 'The Tap Dance Kid'] to his mother and father.''

Compared with Nicholas' and Fleming's, Dule Hill's dancing career has been a breeze.

''My brother and cousin were taking tap lessons and my mother was taking ballet, so that's when I decided that I wanted to take tap lessons,'' explains the confident youngster. ''I started taking tap at the Marie Wildey School of Dance'' -- and they called my school, and I auditioned, and that's how I got the part on Broadway.''

Hill began as an understudy and moved into the lead role of Willie during the show's final months in New York.

Despite his youth, he has already given some thought to his future in show business. ''I want to do a TV show that has tap dancing in it,'' He says. ''I've never seen one before.''

Does he mean a variety show?

''I would want it to be more like a sitcom,'' says Hill in a deadly serious tone of voice. His costars crack up.

''A whole lot of kids come to our show, look up at Dule and say, 'Whoa I'd like to do that. I'd like to be up on stage and be like him,' '' says Nicholas. ''Babies, even . . . they just love it.''

''Then you see the parents wanting to go up there took,'' adds Fleming.

Hill concurs. ''A lot of people hell me that they're trying to get their kids to dance but the kids don't want to. But when they see the show, they just have to dance.''