I don't personally care whether Rudy Giuliani's daughter had joined the One Million Strong for Obama group on Facebook, because it doesn't constitute an endorsement in the sense that the press has asserted.
Friending someone isn't the same as saying you want them to be your president. And candidates' sons and daughters have always had friendships that cross party lines, which is one of the reasons that the United States has remained whole for so long.
However, the reality of the transparency in social networks does make the normal differences of opinion in a family plain to everyone who cares to look for them. Candidates' family and friends have never agreed 100 percent with every opinion or policy of a would-be president. Not even elected presidents have their families marching in lock-step with them. Two of Ronald Reagan's kids were and remain political polar opposites of their father. That didn't mean he was a bad president. The man's decisions on some important issues demonstrated that.
Social networks and the preferences and decisions made through them are going to be interpreted by a country deeply divided about many issues as evidence that can be used in making a decision about the candidate's ability to lead. There is a stupid idea that if a candidate can't make their kids cooperate with them, they can't lead the country or a county or even the dog pound.
In fact, the kids' opinions are their own and shouldn't be a faithful reproduction of their candidate parent's. It would be downright unnatural if families didn't evolve their political opinions. We should leave them to have those opinions without turning it into a national issue, though we won't as long as social networks treat personal data and preferences as a binary all-or-nothing act of publication.
Some nuance is needed, not just among the press, who should have known better than to see Caroline Giuliani's joining One Million Strong for Obama as an endorsement, but among social networks that ought to give people the ability to explore and join groups without always making those actions public.