Between the two of them, they've got 15 kids (five are hers; 10 are his -- it's the second marriage for both), the kids' 15 spouses, 47 grandchildren, and one great-grandchild. (So far.) Keeping track of all those birthdays, graduations, Communions and confirmations takes a nimble mind and a knack for numbers. (A master list helps.) Thanksgiving has to be outsourced. (A 28-pound turkey and a few smaller ones for backup.)

In 23 years of marriage, they've packed in big highs, big lows, big love. But time's whipping by, and while they can, they want to create memories. Scratch that. They want to create one major memory, one that'll last.

Which is why the Marty McNamara-Jean Tyler clan is rattling up I-95 in a chartered bus filled with 52 family members ages 5 to 84, a bemused driver, a DVD player showing movies, and enough doughnuts and coffee to keep the kids distracted and the grown-ups awake (i.e., a lot). They leave Kensington at 7 a.m. Saturday as the sun is coming up, and head toward New York, where Radio City and the Rockettes await them.

But let's be clear about one thing:

"It's not about the Rockettes," says McNamara, the family patriarch, looking hale and rosy-cheeked at 84. "It's the bus. The travel. Broadening a child's exposure. . . . This is a once-in-a-lifetime thing. There are no second go-rounds.

"Unless," he says, slapping the shoulder of his grandson Seamus, "one of our grandsons becomes very rich and carries on the tradition."

The whole thing was Jean's idea. She thought it would be great to bring as much of the family together as possible for an adventure in bonding. Marty asked her, do you realize how many people that is? Yes, she said, what of it? In September they sent out a letter with a proposal: All of them, on a bus, from Kensington to New York and back. One day. Everybody together. Their treat. Marty suggested they all wear name tags to keep track of one another. "Absolutely no," Jean told him.

"We all know each other," says Jean, 72.

(Still, names do slip the mind. On the bus, a pretty teen mutters, as if to herself, "That woman in the red sweater. I forget her name, but she's a relative.")

Some of the kids and grandkids couldn't make it. Some live too far away, in California and in Wisconsin. One grandson who lives in Silver Spring got sick at the last minute. And the great-grandchild, at a year and some change, is too young. But a slew of them made it: Marty, Jean, eight of his kids, two of hers, nine in-laws and 31 grandkids. And here all of them are, hanging together, having a grand old time.

This is an Irish Catholic clan, with an emphasis on the Catholic. (How else do you think I got so many kids?, Marty volunteers. His priest, he says, didn't even approve of the rhythm method.) Which means that Marty starts things out with a prayer, standing in the middle of the aisle, holding the luggage rack for support.

"Our Father who art in heaven," he begins, and everyone chimes in, even the preteens reading the teen mags with the quiz about how to know if you and your BFF (Best Friend Forever!) are really destined to be BFF. (The quiz says yes.) Afterward, some of the teens plug in earphones and zone out, staring out the window at the countryside whizzing by. The ones who're new to high school stand up in their seats, bragging about which one's school has the better cheerleaders. Cups of coffee and hot chocolate are passed from back to front. Orders are scribbled down for dinner on the way back: Turkey or ham and cheese on rye? Dijon or mayo?

The excitement starts to pick up palpably as North Jersey's industrial vista rolls into view. They zip through the Lincoln Tunnel and into midtown Manhattan, where the bus pulls in, right on the block facing Radio City Music Hall. It's just after 11. Everybody's got until 4 to explore the city before meeting up for the 4:30 show.

"This is where we fracture," Marty says as he and Jean meander down Avenue of the Americas, watching fondly as their kin scatter like sprinters out of the starting block. Some head down to Ground Zero. Others dip into St. Patrick's Cathedral just in time for Mass. Others hit Macy's Herald Square to check out the Christmas windows. Still others head off for ice-skating at Bryant Park. And, of course, they shop.

And what will they, Marty and Jean, do until showtime?

Marty shrugs, smiles.

"Hold hands."

When they first met, Marty was a widowed lawyer and a former member of Hubert Humphrey's vice presidential staff. Before his first wife died in 1978, she told him that he needed to remarry in six months. How else was he going to take care of all those kids? She gave him a list of appropriate widow friends to consider. He thought she was nuts.

Two years later, he met Jean. She was a divorced single mother of five who needed an estate lawyer. He fit the bill.

At first, it was all business.

"I thought she was pretty," Marty says, "but at 61, you don't entertain thoughts about getting married."

"He called me four times before I said yes" to a date, says Jean, who worked in the registrar's office at Georgetown University's medical school.

So what made her say yes?

"I don't think I've ever met a man as kind and thoughtful as he. He just embraced my children."

They wed in 1982. Some of the kids were thrilled for them; others less so. But from the start, Marty and Jean made a pledge: "We call them all ours," Marty says. "Her children would be mine, and mine hers."

"We had dinners and cookouts," Jean says, "trying as hard as we could to blend everyone. And it worked."

Says her son, Richard Tyler, 47: "My mother was facing her whole future alone. Then she met Marty and fell in love. Now we don't have to worry about her being alone." He looks around at the crowd of McNamaras and Tylers.

"Ever."

Along the way, they experienced tragedy. Jean's oldest daughter died of breast cancer, leaving behind two young ones. And last year, Marty's youngest, Kathy, nearly died of a brain aneurysm, the same malady that felled his wife.

"It's not a family if the only thing a family has is celebrations in New York," Marty's daughter, Eileen Rice, 55, says. "It's not just, 'Oh, you have a big crowd at Christmas.' In order for a family to stay strong, there's a lot of reaching out."

By 4:30, his and hers are camped out in seven rows in the third mezzanine at Radio City, checking out the Christmas Spectacular. They watch bears en pointe prancing around to the strains of Tchaikovsky's "Nutcracker Suite"; Santa communicating to Mrs. Claus via mobile fax; and the Rockettes taking on many incarnations, from toy soldiers to Santa clones to glamorous snowflakes. Some of the grandkids nod off. Marty gets all teary-eyed at the Nativity scene complete with live camel and sheep. And at the show's end, he stands up and tips his baseball cap at his family. They all applaud.

Afterward, they walk down the stairs of Radio City Music Hall, holding hands, Marty clutching the banister. He starts singing, "I'm dreaming of a white Christmas . . ." and she picks it up on the second line, and this is how they make their way down the stairs, step by step, line by line, focusing on each other and not on the crush of humans, shoving and pushing to get out.

Back on the bus, the grown-ups in the back slap deli meat on bread, and pass the sandwiches up. One of the grandkids pops the movie "Elf" into the DVD player. Kids sprawl out on their parental laps. When the actors in the movie start singing "Jingle Bells," they sing, too.

Marty and Jean walk up and down the aisles, plopping down in this seat and then that, chatting everyone up. Someone says thanks for the memories, for the day, for everything.

"With this," Marty says, "my greatest pleasure is your pleasure."

Martin and Jean McNamara, far right, pose with 50 members of their family outside Radio City Music Hall. They took a bus from the Washington area to see the Rockettes.Taking steps to celebrate the season: The Rockettes are a holiday tradition,

and and a trip to see them is now part

of the lore of

Martin and Jean McNamara's family. Tom McNamara and daughter Lorraine, 6, take a photo outside Macy's in Herald Square. At right, Martin and Jean McNamara leave Radio City Music Hall after a Christmas Spectacular attended by 52 family members.

Upon arriving in New York, the family split up to explore Manhattan, with time for shopping before the show. At left, Lorraine McNamara looks around the Macy's toy department after having a peek at the store's Santa Claus. Above, Peggy McNamara takes in the sights along Avenue of the Americas in midtown.