From ABCNews:
“Let me be a clear as possible: I have said before and I will repeat again, I think people’s families are off limits,” Obama said, “and people’s children are especially off limits.
“This shouldn’t be part of our politics,” he continued, “It has no relevance to Gov. Palin’s performance as governor, or her potential performance as a vice president.
“And so I would strongly urge people to back off these kinds of stories,” he said. “You know my mother had me when she was 18, and how a family deals with issues and, you know, teenage children, that shouldn’t be the topic of our politics and I hope that anybody who is supporting me understands that’s off limits.”
Point taken (at least by me).