Children can point out hypocrisy, and lots of our norms are hypocritical.
This is triggered by a brief post on Kottke.org, where Jason writes, in partial explanation of a decrease in soda consumption in the US:
I've been a dedicated soda drinker1 since at least high school. But this summer, I started cutting back. The big reason is that my kids are getting old enough to read labels and wonder why I'm consuming so much sugar, the little blighters. "All that sugar is not good for you, right Daddy?" they would say. And they're completely right of course and I couldn't argue with them on that point, so I've been drinking a lot less of the stuff. I haven't cut it completely out of my diet but I treat it more or less like every other food or beverage I consume: everything in moderation.