I think that children(under 18) of politicians should be off limits or at least handled lightly. It should be remembered that children(especially those younger than 17) have no say in whether or not their parents run for office.
The line has been a little fuzzy at times. With the rare exception of Glenn Beck, (who was soundly criticized for remarks made on his radio show) everybody avoided touching the Obama daughters. Bush II’s twin daughters were in their late teens as stories of their partying antics, (and giving their secret service detail migraines) began circulating. Robot Chicken regularly made fun of them.
Obama’s children were much younger than Bush II’s.