All of them are attractive and they have shot spoof videos lampooning rival campaigns. These have included mocking a Herman Cain ad, where they drew moustaches on themselves to mimic Cain's campaign chief of staff, and sang a parody of Justin Timberlake's SexyBack that hit at Cain's economic plans.
On Twitter the Huntsman girls have amassed a following of more than 20,000, giving a rare prominence to a campaign that has otherwise struggled to attract media attention. They have even been profiled in the highbrow New Yorker magazine and hosted a live web chat with readers of the Boston Herald.
But it is the Romney clan that has really hit the headlines and used its children to maximum effect. As their father has campaigned in Iowa and New Hampshire, four of the Romney boys - Josh, Tagg, Matt and Craig - have made regular appearances at events and in front of the TV cameras, helped by the chiselled good looks they share with their parents.
Of course, like the Huntsman girls, it is their collective movie-star looks that get noticed, especially by apparently fascinated journalists.
"Romney's sons are quite handsome. Just saying," tweeted CNN producer Danielle Dellorto recently. Scott Stossel, deputy editor of the Atlantic magazine, went a step further and joked on his Twitter feed: "Huntsman daughters and Romney sons should get together and breed, creating a super-race of astonishingly beautiful Mormons."
Elsewhere in the race, Rick Santorum's daughter, Elizabeth, works on her father's campaign team as a part-time staffer.
Santorum has seven children. The former Pennsylvania senator has a campaign poster showing the beaming candidate posing with his wife and their brood and calls his show the "Faith, family and freedom tour".
Several of Ron Paul's children act as campaign "surrogates", doing media interviews on behalf of their father. The most prominent is Senator Rand Paul, who is a major figure in the powerful Tea Party movement.
Experts say that putting family members into the public eye - especially large numbers of good-looking children - sends a clear political message, especially to Republicans. It is making an unsaid promise that the happy and fertile private life on display will translate into a virtuous period in office.
"It is a theme of private virtues becoming public virtues. They are sending the message that the basis of the political system and the basis of society is the happy household," said Gronbeck.
With Romney, Huntsman and Santorum, it is also a firm expression of their religious convictions, as all are devout Mormons or Catholics whose faiths put an emphasis on having large families.
Stressing the existence of a happy family also strikes a chord with a core element of the Republican base, social conservatives, who have often been left out of the American political conversation in the wake of the Great Recession which began in 2007. While economic issues have dominated debate since then, the so-called "values voters" have sometimes felt sidelined. But each campaign knows a public display of family by a candidate may go some way to winning over a group that is still a vital part of the Republican Party's activist base.
"You have to be seen engaging in family-related things - it is the kissing babies side of campaigning," said Gronbeck.
Of course, putting children on the campaign trail can also cause problems, especially when using social media, which can often be unregulated by overworked campaign aides. The Huntsman girls clearly have an issue with moustaches. They reportedly irked their father's staffers with some of their tweets, including one that mocked Obama aide David Axelrod for having a bushy upper lip.
Another lampooned Romney's lack of foreign policy experience, saying eating at Panda Express, an American Chinese fast-food chain, "doesn't count".
The Romney sons have also strayed off-message, notably when making a dubious joke about the reality of Obama's birth certificate. There was a swift apology. In this race, the sons and daughters need to be politically savvy too.Observer
Relative difficulties
Family can have its drawbacks, as some politicians have discovered in the push for office.
Roger Clinton
President Bill Clinton had enough troubles in his time in office from his own personal failings. But his half-brother, Roger Clinton, added to the mix as a hard-living musician. He served a year's jail for cocaine possession and was arrested for drink-driving and also challenging a nightclub doorman to a fight.
Neil Bush
The Bush clan was always conscious of its image, producing two Presidents named George and a Governor of Florida in the shape of Jeb. But Neil, a sibling of George W. and Jeb, hit the headlines for his divorce. In a bitter legal spat, details emerged of Neil's use of high-class escorts in Thailand and Hong Kong. As Rick Perry might say: "Oops."
Billy Carter
President Jimmy Carter's young brother, Billy, was a bit different from his humble, devout elder sibling. He revelled in the image of a hard-drinking Southern redneck, even promoting a brand of beer called Billy Beer.
