I think of politics as a war; one where family members should be left out. the attacks aimed at Palin's kids are be akin to attacks on Kitty dukakis or Betty Ford for their alcoholism.
Excluding very personal questions like the one you posed, if the family members choose to insert themselves into politics then they have the right to be judged as everybody else. I could see if you're a little kid or a teenager who simply supports your parents, I mean who wouldn't?
But if you're a full fledged adult who has your own opinion, freely gives your own opinion into the mass public media, and expect not to have some response back whether it's positive or negative then that's crazy. The same goes not just in politics but the entertainment industry or really anything for that matter.
You can agree with that can't you Elvis? Also, to reflect your edit, I agree nobody should attack Palin's CHILDREN. However, when you have a kid, you're not really a kid anymore.