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The White House, Pete Souza, file, Associated Press
FILE - In this Sept. 4, 2012 file image originally released by the White House, President Barack Obama and his daughters, Malia, left, and Sasha, watch first lady Michelle Obama speak at the Democratic National Convention on television from the Treaty Room of the White House. For many TV viewers, who may not have seen much of the Obama girls since election night or the convention four years ago, it will surely be a surprise to see how much the Obama daughters have grown when they appear in Charlotte Thursday night.

NEW YORK — Who are those tall, willowy young women with Barack and Michelle Obama — and where'd they hide little Sasha and Malia?

Four years is a long time when it's a half or a third of your life, and so TV viewers who haven't seen the Obama girls much since 2008 may be truly startled at just how much they've grown when they appear later Thursday after their father's speech.

"It's kind of like coming home for Christmas after many years," says Douglas Wead, author and expert on presidential offspring. "People are going to be very surprised."

"We're really going to be seeing them as young women," says Sandra Sobieraj, a correspondent for People magazine who has long covered first families. "It will be stunning, because we don't see them regularly. There hasn't been a steady stream of images to relate to."

Malia is now 14, and this week started (gasp!) high school. Sasha is 11, now in sixth grade. Malia is nearly as tall as her parents: "Even though she's five-nine, she's still my baby," Obama said a year ago. As for Sasha, her parents told People last month that she's grown a foot in the last year, and suddenly resists cuddling.

It's hard to believe that only four years ago, at the 2008 convention in Denver, Sasha, then 7, fidgeted in her purple pinafore-style dress, little white barrettes on either side of her head. "Daddy, what city are you in?" she called out in a high-pitched voice as her dad appeared on a huge video screen the night of Michelle Obama's speech. "I love you, Daddy!" called out Malia, 10, looking a bit older in a two-toned dress with straps.

Then came the iconic images on election night, when the family, color-coordinated in red and black, celebrated Obama's emotional night in Chicago. There was Sasha in a black party dress, bounding gleefully up into her father's arms, planting a big kiss on his cheek — a reminder that young children were about to live in the White House for the first time since Chelsea Clinton, Amy Carter, and before them, the younger Kennedy kids, Caroline and John.

And of course there was the inauguration. Who could resist the sight of Malia Obama, in a periwinkle-blue coat and fluffy black scarf, snapping pictures from her enviable perch on the inaugural podium?

Just the night before, she and Sasha, whose inaugural outfit was a light pink coat, had danced onstage with the Jonas Brothers — a perfect example of how, as much as her parents vowed to keep their lives as normal as possible, they were truly celebrities from Day One.

For the president and first lady, protecting their privacy was an evolving skill. Candidate Obama quickly regretted, for example, an all-family interview granted to Access Hollywood.

Once the family arrived at the White House, stricter arrangements were in place. The news media traditionally respects the privacy of a president's young children and doesn't photograph or report on them unless they are in a public setting with their parents.

Yet the couple constantly talks about their kids. At times the president has embarrassed them, as when he told an audience that Malia once got a 73 on a science test. (He later apologized.)

Two years ago, when Malia Obama first went to summer camp, the White House discouraged any mention of it in the media, even though Obama mentioned it in interviews. And recently he revealed the state where both daughters had spent a month at camp — New Hampshire.

"They just love talking about their girls," says Sobieraj. "They get genuine joy from them, and so they talk about it. To a degree that makes the staff uncomfortable, because the line is shifting."

Other White House kids have led much less public lives. Jackie Kennedy was so concerned about keeping her kids out of view that she organized kindergarten for Caroline inside the White House. (She was out of town when her husband allowed those famous photos of Caroline and John in the Oval Office to be taken, Wead says.)

And Bill and Hillary Rodham Clinton were extremely protective of Chelsea, who entered the White House at an awkward stage. Her parents were furious when Mike Myers referred to their daughter in an insulting way on "Saturday Night Live"; the comic later apologized.

Whereas many White House children seem to suffer some sort of embarrassment or scandal, the Obama girls have had none, not even a bad hair day, it seems.

"Compared to other White House families, this is clearly the most functional," says Wead, ho chronicles a host of misfortunes of White House kids in his book, "All the President's Children." ''This has been one of the most successful stories."

Clearly one reason is that the Obamas spend so much time with their kids. The president has coached their teams, and faithfully attends games and parent-teacher conferences. The first family is known to have dinner together in the White House most nights; Michelle Obama in her convention speech evoked the image of the family "strategizing about middle-school friendships."

That will likely help the president avoid the guilt that, Wead says, overcame Ulysses S. Grant on the occasion of his daughter's White House wedding. She left on her honeymoon, and Wead says the president then collapsed on her bed and wept.

"He had been so busy as president that he felt he had missed her life," Wead says. "It all had happened too fast for him."