Donny and Marie Osmond in "Donny and Marie: Christmas at the National." (Jeremy Deputat )

A standing ovation came at an unexpected moment Tuesday night as Donny and Marie Osmond began their week-long stand at the National Theatre. A video montage during a low-key ballad chronicled the careers of these ultimate showbiz kids from their current incarnations as Las Vegas mainstays back to their roots as 1970s teenage chart toppers and prime time TV variety show hosts.

There they are with everyone from Michael Jackson to Sonny and Cher to Milton Berle. It’s 50 years of entertaining for them both and 60 albums now for Donny, decades of ups and downs and somehow a near-permanent place in pop culture. Suddenly it feels monumental: They aren’t just cheery young singers still making good. They’re like a national park.

But, aw, heck, they’re still just Donny and Marie, and during their two and a half 2 1/2 hour “Donny & Marie: Christmas at the National,” they ease into the brother-sister bickering bits the way they’ve always done.

“You’re a butt,” the ever-feisty Marie plaintively gripes at big brother Donny when he pulls a prank on her. (The tables turn again and again; you remember the routine.) When they swing into song, a big video screen amplifies their beaming faces as lithe dancers gyrate all around. The stars look great, sound terrific and move like pros.

Better yet, they connect all night with a loyal fan base that has followed them since the days of Donny’s “Puppy Love” and Marie’s “Paper Roses.” They hopped into the crowd again and again, joking and flirting and signing memorabilia, such as the vintage Donny & Marie doll set a grown woman toted to the show.

The Osmonds know better than to take their fame for granted, so while the evening is appealingly playful, the act is also admirably hard-working. Marie gallops merrily through a country medley of Christmas tunes, flanked by cowboy dancers in sleeveless shirts as she belts “Jingle Bell Rock,” “Run, Run Rudolph” and “Honky Tonk Christmas.” Her voice is at its most commanding in this Nashville style, and she growls with a nicely dirty edge as she cavorts in boots and a big black hat.

Donny’s struts and swivels are creamy and fluid as he trots out his 1989 hit “Soldier of Love.” He tore a glute winning “Dancing with the Stars” in 2009, but he looks sharp here and in a mashup of celebration tunes (framed by the Rare Earth hit “I Just Want to Celebrate”) that scratches his itch to rock. He still makes everything he sings sound easy, and the duo’s inevitable “Little Bit Country/Little Bit Rock n’ Roll” medley puts a high-spirited “Santa Claus is Comin’ to Town” in his wheelhouse and “The Christmas Song” in hers.

The six-piece onstage band generates a lot of flavorless tinny synthetic sound, unfortunately, but the harder this keyboard/guitar based outfit drives, the better it gets, with the upbeat country-rock duet “It’s A Beautiful Life” (from the 2011 album “Donny and Marie”) as a highlight. On the other end, what’s Marie doing singing Mozart’s “Ave Verum Corpus” in a shadow so dim you can’t even be sure it’s her? Choral voices come from everywhere and nowhere; it’s a piping-hot mess.

Not that that marred anything. They are Donny and Marie, a form of stainless steel, even with Marie grousing all night about the monitors and sound levels (first night kinks, you hope) and with the evening hitting a couple of lulls (their Vegas act is reportedly a tidy 90 minutes). The flagging passages are wiped out as, say, Marie zips through “Boogie Woogie Bugle Boy,” strolls into the audience to draw luscious kiss marks on men’s heads with a lipstick, or emerges in yet another tight spangly dress and pair of fancy boots; she changes flashy costumes about every 10 minutes.

Donny, in a trim suit and tie, frequently juices the crowd by cruising the aisles, slapping hands and planting kisses. A woman in the front row grabs him for a long squeeze; she gushes that she met him long ago when she was 15 and says she wanted to marry him. Donny tells her how wonderful that is. With his arm still around her neck, he looks into her eyes and adds, “You know, I’m singing a song here.”

Well, he is, and he isn’t. And the cocktail of painstakingly maintained platinum talent and warm-hearted celebrity bonding is perfect.

‘Donny & Marie: Christmas at the National’

Through Dec. 7 at the National Theatre, 1321 Pennsylvania Ave. NW. Tickets $53-$228. Call 800-514-3849 or visit