The Mann is alive with . . .

Let's start at the very beginning, a very good place to start.

The four fetching von Trapp Children, who perform tonight at the Mann Center with Peter Nero and the Philly Pops, are the great-grandchildren not of Christopher Plummer but of the true Baron von Trapp, who escaped Austria in 1938.

The Montana-based siblings, ages 12 to 19, travel in jeans and Keds, not their great-grandmother Maria's dirndls, though they wear them on stage. They are adorable, fresh-faced, forthright and without airs.

Justin, 12, appears in lederhosen for performances, but his shoes, in truth, are Skechers. They sing traditional folk songs, as well as seven songs from the The Sound of Music, including "Edelweiss." How could they not?

"Edelweiss," incidentally, is not a traditional Austrian folk song, lilting as it is, but the last song written by the great Oscar Hammerstein II with Richard Rodgers. Hammerstein died in 1960 in Doylestown. He never heard Julie Andrews' gorgeous voice embrace the song in the 1965 movie; Mary Martin played Maria when the show opened on Broadway in 1959.

The von Trapps' true grandfather, Werner, whom they call Opa, is named Kurt in The Sound of Music and is supposed to be 11. In reality, Werner escaped Austria when he was 23. "They condensed a 12-year period into three months," says Melanie, 17.

Six years ago, the siblings began singing a cappella as a way of cheering up their Opa as he recovered from a stroke. It must have worked because Opa, a retired Vermont dairy farmer, is very much alive at age 92, and the von Trapps have been touring ever since.

Sometimes, like tonight, they perform with an orchestra. Often, it's simply their voices, ranging from alto to first soprano, and a piano. The group is very low-maintenance.

Touring - they did Europe and Japan earlier in 2007 - takes up nine months of the year. First home-schooled by their parents, Annie and Stefan, a stonemason, they now travel with a tutor. They're rarely home in Kalispell.

Here's the thing about The Sound of Music: Everyone has seen it. Everyone has seen it a billion times.

"We grew up with it." Melanie says. "We didn't realize how it affected everyone else," says Sofie, 19. "We thought it was a great musical, like Oklahoma."

Oklahoma is great but it doesn't have kids or curtains or raindrops on roses and whiskers on kittens. It doesn't solve a problem like Maria.

No one is dressing up as lonely goatherds or tea bags to attend raucous Oklahoma sing-alongs as they do for The Sound of Music. If you haven't attended one, you must. It's the most fun you can have yodeling.

The von Trapps have participated in a few sing-alongs, their most memorable being before 18,000 acolytes at the Hollywood Bowl.

Sofie and Melanie stayed at the original von Trapp home in Salzburg, now a convent - sort of coming-full-circle given that Maria Kutschera began as a novice in the nearby Benedictine Abbey at Nonnberg.

"It was really cool," says Sofie.

"Absolutely," Melanie echoes.

The four von Trapps get along exceptionally well. "It would be horrible if we didn't," Sofie says.

They like to play practical jokes on each other. When the toilet backs up, Sofie is fond of calling for help, then fleeing the premises so Amanda, 16, hasn't a clue what a man with a plunger is doing at their door.

"It's absolutely brilliant," Sophie says, her long blond hair tumbling over her shoulders. For performance, it's always in two front braids. Amanda curls her darker hair for the stage. She scrunches her nose at the thought.

The von Trapps love music. They're less enamored of theater. "We're not performers so much as musicians, singers," says Sofie.

"It's cool to be able to be ourselves and travel the world," says Melanie.

Once, only once, have the siblings actually acted in The Sound of Music, in Raleigh, N.C.

The girls performed the roles based on their great-aunts - though not Liesl and the kissing stuff - while Justin portrayed his grandfather.

"I just hope he wasn't there," Justin says, shaking his head at the thought.

While they love performing traditional folk music, American and Austrian (though their German, they confess, is feeble) and haven't tired of The Sound of Music catalogue, the siblings have different tastes in other music, and varying long-term career plans.

Sofie, the eldest, loves Van Morrison, the Who and Celtic music. She has been accepted at Boston's prestigious Berklee College of Music, where she plans to study the music business. "The smartest thing I need to know is contracts. I'm interested in musical production for albums," she says.

Melanie is a fan of Celtic music, the bluegrass band Nickel Creek, and "any music that's really well done." Unsure of college plans, she intends to continue performing.

Amanda is "all country. I love Tim McGraw, George Strait." She hopes for a job in law enforcement, studying in Washington, D.C.

And Justin, who loves Celtic music and bluegrass? Justin's 12. He's happy traveling the globe, singing with his sisters, eating pizza in the hotel.

And then, before you know it, there's a sad sort of clanging from the clock in the hall, and the bells in the steeple, too.

It's time to say so long, farewell, Auf Wiedersehen, adieu - adieu, adieu, to yieu and yieu and yieu.

Music

The von Trapp Children

With Peter Nero and the Philly Pops tonight at 8 at the Mann Center for the Performing Arts. Tickets $20-$70. Information: 215-893-1999 or www.phillypops.org