Yes, the candidate knows that the tabloids and other media will go after their family. But the candidates have basically followed an unspoken "gentleman's agreement" of sorts not to go for the family members themselves. Hillary was an exception because she was obviously thinking she was on the ticket, as well. But not the kids.
Kerry and Edwards have demonstrated their lack of class over and over with issues like Mary Cheney. What if Bush had said "There are many more thousands of young people killed in auto accidents than in Iraq, as Senator Edwards and his wife can verify since their own son was killed in a crash instead of in a war." That would be disgusting, as was Kerry's inane remark.
My thinking is more along the lines of Harry Truman in regards to his daughter Margaret.