Ronald Reagan’s daughter posed for Playboy. President Bush’s twins were caught drinking when they were under the legal age. But the daughter of the Republican presidential front-runner, Rudy Giuliani, has really crossed the line. She is not just supporting a rival candidate — she’s backing a Democrat.

Caroline Giuliani, 17, became the latest in a long line of children to complicate their parents’ political ambitions when it emerged yesterday that she had signalled her support for Barack Obama rather than backing her father’s White House bid.

Ms Giuliani’s support for Mr Obama, in an entry on her online Facebook profile, threw a fresh and unwelcome spotlight on the deeply strained relationship that the former New York mayor has with his two adult children.

Mr Giuliani, currently the leading contender for his party’s nomination, is estranged from Caroline and her brother, Andrew, 21, the children from his second marriage to Donna Hanover. In a now-infamous episode, Ms Hanover discovered that her husband was leaving her when he announced it at a press conference in May 2000.

His son made clear in an interview three months ago that relations with Mr Giuliani’s third wife, Judith Nath-an, were not good, that he would not campaign on behalf of his father and that they were barely speaking. Neither child is mentioned on the former mayor’s presidential website. “My daughter I love very much,” Mr Giuliani said yesterday, but added: “I don’t comment on children because I want to give them the maximum degree of privacy.”

In stark contrast are the five sons of Mitt Romney, the former Massachusetts Governor and a Republican rival to Mr Giuliani. The most popular feature on Mr Romney’s website is his children’s blog, Five Brothers, in which they appear as a wholesome cross between the Osmonds and the Brady Bunch.

There is Tagg Romney, 37, who loves Billy Joel; Matt, 35, would like to meet Winston Churchill; Josh, 31, likes water sports; Ben, 29, has one hero: “my dad”; and Craig, 26, is reading A Mormon in the White House?, a reference to the family’s religion. All five are married. All but one have children.

Meanwhile, with Hillary Clinton extending her lead in the polls over Mr Obama in her quest for the Democratic nomination, attention is once again turning to Chelsea Clinton.

Now 27, and a hedge fund manager in New York, Miss Clinton appears regularly with her parents at fund-raising events — recently she helped to raise more than $20 million (£10 million) for the Bill Clinton Foundation – but has so far refused to speak at her mother’s campaign events.

She is a campaign veteran, however. She first appeared, aged 12, in Mr Clinton’s Man From Hope video during his 1992 White House bid.

Mr Obama’s daughters — Sasha, 5, and Malia, 8 — are slowly being introduced to the public by a candidate who has been made painfully aware of how presidential politics can bring unwanted scrutiny. In March a self-confessed paedophile was forced by Mr Obama’s lawyers to remove from his website a family photo of the candidate with his wife and children.

With multiple marriages among the Republican candidates — except Mr Romney, married for 40 years to his childhood sweetheart — there are plenty of children to help out. Fred Thompson, 64, the former senator and actor, has two surviving children from his first marriage and two from his second marriage.

John McCain, another Republican contender, has seven children from his two marriages. He rarely mentions them, but his son Jimmy is hard to ignore. Mr McCain is a staunch supporter of the Iraq war and Mr Bush’s “surge” strategy, and Jimmy, a Marine, will soon deploy to Iraq. He has been standing alongside his father at recent campaign events.

Behaving badly

Patti Davis daughter of Ronald Reagan, renounced father's name, admitted drug use and posed naked with man in 1994

Jenna and Barbara Bush charged with underage drinking in 2001

Bryan Frist Senate leader Bill Frist’s son, wrote: “I was born an American by God’s amazing grace. Let’s bomb some people.”

Paul Dean Democratic candidate Howard Dean’s son, arrested trying to break into club in Vermont

Albert Gore III son of presidential candidate Al Gore, charged with drug possession in 2004.

Times Recommends

• Please help: maimed children of war want their lives back
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president