WASHINGTON -- President Barack Obama and first lady Michelle Obama fiercely protect the private lives of their daughters, Sasha and Malia, as they raise the girls in the fishbowl that is the modern White House. Yet, the Obama girls – ages 13 and 11 – increasingly are making public appearances: starring in remarks by their father, appearing in a campaign video celebrating Father’s Day and now in a campaign ad that’s airing in seven battleground states.

The bump in visibility comes as President Obama uses the girls to personalize his image and his thinking on a range of public policy issues, from explaining why he placed a phone call to a college student assailed by radio talker Rush Limbaugh to his decision to support gay marriage.

"It wouldn’t dawn on them that somehow their friends’ parents would be treated differently," Obama said of his daughters as he explained his switch to supporting same-sex marriage. "It doesn’t make sense to them and, frankly, that’s the kind of thing that prompts a change in perspective."

Politicians often showcase handsome families, in part to humanize themselves. Mitt Romney’s five good-looking sons recently jousted with late-night TV host Conan O’Brien in a bid to show their father as a fun-loving guy. Former Utah Gov. Jon Huntsman’s telegenic three daughters got nearly as much attention for arch videos and a zingy Twitter account as did the onetime Republican presidential hopeful’s campaign.

And the Obama girls?

“They’re the most popular unit of the family,” said Tom Jensen, the director of Democratic-leaning Public Policy Polling. “Who doesn’t like the girls?”

His firm surveyed the girls’ popularity in 2009 and found them with numbers politicos would covet: a 54 percent favorability rating and an unfavorable standing of just 5 percent, numbers that he thinks are unlikely to have moved much.

Jensen notes that family is a big factor for President Obama, whom polls show people like even if they’re not crazy about his stewardship of the economy.

“Children have a kind of humanizing impact, and that’s really what Obama needs,” Jensen said. “Voters feel like things haven’t changed as much as they wanted. The economy still is not where they wanted it to be. He needs people to vote more on whether they like him or not, regardless of his record of accomplishment.”

A Gallup poll this week found Obama with a wide lead over Romney when it comes to personal likability.

“With that small swath of swing voters that everyone wants, if something gets people to think about Obama the man, as opposed to Obama the guardian of the economy, he’s in better shape,” Jensen said.

The news media have largely hewn to an understanding that the Obama girls are off-limits for coverage, unless they’re with their parents at a public event. When a wire service reported a spring-break trip to Mexico by one of the girls in March, the White House urged websites not to run it.

“The president and first lady are loving parents who have made shielding their daughters from the glare of the media spotlight a high priority and are pleased by the respect that media, by and large, has shown for their daughters’ privacy,” said Josh Earnest, the principal deputy White House press secretary.