Are we protecting our kids too much?

Over at Half Changed World, ELB writes:

Coming from our little ad-free world, it was a real shock to be visiting my parents Columbus Day weekend and to encounter all the commercials in the baseball games. ... Since D doesn't see commercials all the time, he was fascinated by them.

Our kids don't watch too much television either and when they do it is usually PBS which only has sponsor messages at the end. I sometimes wonder if we are over protective -- how would they react when they see something we have been sheltering from them for the first time? Curiosity? Over react? I sometimes think that age limits on alcohol use is a little like over protecting but I'm not fully convinced yet. Ideally, if it is something important that we are protecting them from, we would talk about it little by little over time so that they adjust or get used to the idea. For TV ads, I guess we would say what? That they are trying to sell us something that we may not want?