Their appearance will be a rare one: unlike in earlier political races, they have barely been on the campaign trail this time. They have spent this summer swimming, playing sports and attending camp in New Hampshire. They are no longer the small children who toted little pink bags with Uno cards and markers at campaign events years ago in Illinois and Iowa. Malia, now 14 and nearly as tall as her parents, is a varsity tennis player with a cellphone. Sasha, 11, who seemed to grow overnight this summer, can chat in Mandarin.
And yet if the Obama girls are bit players in the presidential race, they are also important ones - not as campaigners but as characters, highlighting traits important to their father's re-election hopes: his likability and his family-man image. Voters know about Malia and Sasha while barely hearing them speak, encountering them in Obama advertisements, photographs and campaign videos, and in the nonstop stories told by their parents.
"We're going to be experiencing the first stages of empty nest syndrome," President Obama told Charlie Rose in a CBS interview this summer, before his daughters left for camp. "I get a little depressed."
On Thursday night, they appeared in a video and in person before and after their father's speech, but on Tuesday night, they were here in Charlotte without being here. One of the most memorable images invoked in Michelle Obama's convention speech was that of her husband sitting with their girls at the end of the day, "strategizing about middle school friendships." As she spoke, the White House posted on Twitter a photo of the president and his daughters curled up on a sofa in the White House living quarters, watching Mrs. Obama on television.
The first couple clearly choose the stories they tell about their daughters carefully. The anecdotes are rarely about the celebrities the girls meet or their glamorous trips on Air Force One. If Malia and Sasha have felt anxiety or distress about the scrutiny and security they live with, the Obamas do not say so. Instead, the president and the first lady share upbeat anecdotes that reflect the rhythms of an ordinary American family: the end-of-season basketball tournament that Sasha's team won, her discovery that she liked tomatoes, the girls' enthusiasm for the television show "Modern Family."
The stories are an implicit counter to right-wing charges that Mr. Obama is a threatening figure, a socialist or somehow un-American. "The family seems so utterly normal, the type of people who could be at the soccer game or basketball game," said Steve Schmidt, who managed Senator John McCain's 2008 bid for president.
They are also unique figures in the election, because they seem so innocent compared with the rest of the political world, and because their parents protect their privacy and the news media largely respect that position. "They are a bit of a mystery," said J. J. Abrams, a Hollywood writer-director and Obama donor, discussing how they come across on the public stage. "But they're authentic, and we're starving for that."
So far, at least, the Obama girls have not had a gaffe or an embarrassing moment - a rarity for such well-known figures, especially when it comes to presidential children. Chelsea Clinton was tormented as an adolescent for having freckles and frizzy hair. Barbara and Jenna Bush suffered brief careers as tabloid fodder for their nighttime adventures, though they have recently been far outmatched by Britain's Prince Harry. Malia and Sasha, meanwhile, publicly appear composed, polite and content.
Aides who know the girls say they are disciplined, thanks to their father but mostly to their mother. (Some staff members even joke that they wish they could send their own children to Mrs. Obama's boot camp for training.) Here are just a few of the household rules that she has mentioned in interviews and other appearances:
-- When the girls go on trips, they write reports on what they have seen, even if their school does not require it.
-- Technology is for weekends. Malia may use her cellphone only then, and she and her sister cannot watch television or use a computer for anything but homework during the week.
-- Malia and Sasha had to take up two sports: one they chose and one selected by their mother. "I want them to understand what it feels like to do something you don't like and to improve," the first lady has said.
-- Malia must learn to do laundry before she leaves for college.
-- The girls have to eat their vegetables, and if they say that they are not hungry, they cannot ask for cookies or chips later. "If you're full, you're full," Mrs. Obama said in an interview with Ladies' Home Journal. "I don't want to see you in the kitchen after that."
After three years, friends and aides say, the Obama girls have fully settled into the White House and have made peace with the quirks of life there. But if their father wins a second term, they will be teenagers in the White House. Four years ago, Mr. Obama liked to say that he was running for president when his girls were young so that the experience would pass over their heads. As they mature, less will be lost on them - good and bad - and they will have to figure out the presidential versions of first dates and college tours.
Meanwhile, one small measure of their popularity is visible on the streets of Charlotte. Near the convention arena, vendors hawk Obama T-shirts, calendars and buttons that feature not just images of the president and the first lady, but of their two daughters as well.