"The Walking Dead" - probably not.
But you're right, most PG-13 films errr, movies are fairly tame.
I think people forget that when you're home, you rule to roost. You can control 100% of your children's world, but to expect that same level of control once you step out into public is unrealistic.
When I was wee lad, I "saw some stuff". I think I saw my first porn when I was 9 (older brothers, parents out of town and brand new BetaMax) - really didn't care because I was happier that I found my soldering iron so I could fix my radio and didn't pay attention, a dead body (headshot!) at my great uncles house -- in fact it was him, my neighbors brains on my dad's Caprice Classic when he fell out of a tree he was trimming, and I'm not an axe murderer or anything.
Well, I don't murder often, but I can be a little sociopathic when it comes to unleashing the BANHAMMER OF THOR.
I'm not suggesting we not filter and attempt to protect children, but those parents need to have a coke and a smile and shut the *mumble* up...
Sometimes you're going to walk into Chuck E. Cheese right before they close to pick up a pizza and the rat's head is going to be off and he might be smoking a doobie. Get over it and move forward.