At their best, some operatives say, adult children are highly sought surrogate speakers, envoys to peer groups such as students, and windows to a candidate's character.
"They play a really important part in giving people a deeper insight into the candidate as a parent and a family person," says Democratic strategist Doug Hattaway, who worked on the 2004 convention that showcased well-received speeches by nominee John Kerry's daughters.
Besides Sarah Huckabee and Cate Edwards, this year's active offspring include Republican John McCain's daughter Meghan, 22, who last week launched an on-the-road blog called McCainblogette.com.
Also in the mix are John Mark Huckabee, one of Sarah's two brothers; Democrat Joseph Biden's daughter and two sons, and Republican Mitt Romney's five sons.
They say they give their parents unvarnished advice and opinions, mostly on style and strategy. "I'm not a yes person, whether it's about a tie choice or a joke," Sarah Huckabee says.
The five Romney brothers occasionally try to get their father "to go a little more casual," says Tagg Romney, 37, the eldest. Aside from the Iowa state fair (Mitt Romney wore shirtsleeves and no tie) and straw poll in August (golf shirt and khakis), they've had little success.
"He is who he is," Romney says of his father. "He thinks wearing the suit and tie to most things is what the office requires."
The difficult child
Cordery says independent-minded progeny could make some voters wonder, "If a president cannot govern his own children, how can he govern the country?"
Yet grown-up children have been the bane of several successful politicians. Alice Roosevelt Longworth was notoriously uncontrollable. Theodore Roosevelt was quoted as saying he could manage the government or manage Alice, but he couldn't do both.
Reagan's children brought a raft of complications. Ron Reagan Jr. and Patti Davis, Reagan's children with wife Nancy, did not share their parents' conservative political views. Davis aired family conflicts in an autobiographical novel and later — after dad was out of office — posed nude for Playboy and appeared in an adult video.
Maureen Reagan, the president's daughter with actress Jane Wyman, ran unsuccessfully in the 1982 Senate primary in California without her father's backing.
"The president made it clear that he did not get involved in primaries," Rollins says.
In 1984, after her father was re-elected, Maureen wanted to be co-chairman of the Republican National Committee. Rollins says committee Chairman Frank Fahrenkopf told him to "stop this."
Rollins says he got up his nerve and told Reagan that his daughter would be "a disaster" in the post. "He said, 'Ed, just be grateful I only have one child who's active in politics.' "
Maureen got the job.
Republican Rudy Giuliani, who is in his third marriage and on strained terms with his two children from his second, is a current example of how private problems can co-exist with political success.
His son Andrew, 21, a Duke University student and golfer, says he won't have time to campaign. Andrew told ABC News in March that "I got my values from my mother," Donna Hanover.
Andrew Giuliani did not respond to an e-mail seeking comment. His father asks voters to "leave my family alone" and judge him by his record. The former New York mayor has led national polls of the GOP field for months.
Sometimes, the career choices of candidates' children can create awkward situations on the campaign trail.