When are the Obama daughters off limits to the public? The answer, apparently, is that it depends. On a few occasions when outside interests have tried to co-opt the popularity of Sasha and Malia _ such as when the Beanie Babies company sold dolls in their images, or when a group advocating nutrition-policy reform made reference to them on District of Columbia billboards _ the White House has swiftly clamped down. And early last year, in a statement, a spokeswoman for first lady Michelle Obama called it 'inappropriate to use young, private citizens for marketing purposes.' But what if the marketing campaign is President Barack Obama's new book? 'Of Thee I Sing: A Letter to My Daughters,' a 40-page picture book aimed at children ages 3 and older, is scheduled for release Nov. 16. The cover features an impressionistic painting of Malia, Sasha and first dog Bo. White House officials say the first daughters are marginal to the content. The book includes tributes to 13 'groundbreaking Americans and deals that have shaped our nation,' according to the book's publishers. Among the 13 are Georgia O'Keeffe, Jackie Robinson, George Washington and Albert Einstein. Using the girls to sell the title _ the second book in a $1.9 million deal for three books, only one of them for children, that Obama inked before becoming president _ is not inconsistent with the policy of generally shielding the girls from public attention, the officials say. 'I think our encouragement is to keep their private lives private,' press secretary Robert Gibbs said Wednesday. Sasha, 9, and Malia, 12, will not be doing any book promotion, he said. In an interview with Sirius XM radio this week, Obama said he was asked to write the book by publishers who thought he 'might have something to say to young people.' The book was initially scheduled to come out in 2006 and explore a portion of Obama's childhood, according to a 2004 news release. The Obamas themselves have repeatedly put the daughters in the spotlight. The book title borrows from an earlier bit of exposure: a Parade magazine cover story that ran a few days before Obama's inauguration called 'A Letter to My Daughters,' featuring their picture. The first lady has included both girls in her anti-childhood obesity and healthy eating campaign, often saying in speeches that an uptick in her daughters' weight led her to serve more balanced meals. Obama, as a candidate, once told Parents magazine: 'A couple of years ago _ you'd never know it by looking at her now _ Malia was getting a little chubby.' Yet when the Physicians Committee for Responsible Medicine tried to do the same thing with a school lunch campaign aimed at reforming the Childhood Nutrition Act, a key priority for the first lady, they heard from the White House. The ad featured a young black girl with a thought bubble asking: 'President Obama's daughters get healthy lunches. Why don't I?' 'When we did the ad, it didn't mention their names, it didn't show their photographs and it was entirely positive,' said Neal Barnard, the group's president. 'I was very surprised to get a call from the White House lawyers saying that in no uncertain terms, I had to take the pictures down. I didn't.' Historian Doug Wead said that, as they continue to put their daughters in the spotlight, the Obamas could find it harder to argue that they should not be written about. Wead said that 'as they get older and more famous they become more of a commodity.' 'You can't say they are off limits and then spoon-feed stories of your own choosing,' said Wead, author of 'All the President's Children.' Still, it is difficult for any presidential parent to fully separate the political from the personal, according to Letitia Baldrige, who served as social secretary in the Kennedy administration. 'I think every president has been aware of the power of children. The Kennedys didn't want the kids talked about at all, they clamped down on everything, but 14 months into the administration, if the children had a story, it came out,' Baldrige said. 'The children were used as a public relations tool and all of a sudden it made the Kennedys very cozy and family-like. It was a whole new way of looking at them.' 