CHARLOTTE, N.C. — On Friday, Malia Obama will be at her desk at Sidwell Friends School for the fourth day of high school — hours after waving onstage at the Democratic National Convention with her sister, Sasha.

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.