I'm one of those who loved the movie. But then I took my son to the theater and my expectations were on the lower side of Cars so I was plesantly surprised.Of course, in the end, it's all up to the parents as to what a child should be allowed to watch, and my wife and I take full responsiblity for that (which is partially why I'm bringing up the topic). I'm intereseted to hear other parent's thoughts on this subject.
Otto... my son is five now and I am clearly on the permissive side of what I watch with him. We've seen just about every super-hero movie together - with the exception of Punisher/dardevil or any of the new batman movies. I draw the line at really gory violence.
There are things kids relate to and find scary and possibly disturbing. I think seeing people suffer is very scary to them. The violence is bad enough but often it's the aftermath that can really be disturbing.
Then there are things we find disturbing that kids have no context to relate. Post-apocalyptic scenarios are an example. You and I know what it's about but to explain Post-apocalyptic Earth to any kid would require a lot of back-story.
I find animated violence... superhero fighting... not so alarming. My son's a boy and we spend a lot of time play-fighting.
We've talked a lot about fighting in real life. I practice martial arts and someday he is liable to as well. He also knows I was the US Army and jumped out of helicopters. He is enamored with all things military.
He's at the age where he relates strength with fighting - and toughness.
Fortunately he has me to guide him through these things. I explain to him in my yoda-like voice... fighting make not one tough... tough is the ability to endure, not to fight.
In fact, not fighting often makes you far tougher than someone who is quick to fight.
I'll add that cleaning his room, even if he doesn't want to, is endurance and makes him tough. Walking in the winter to get groceries even though he'd rather we take the warm truck... that's endurance, that makes us far tougher than someone who fantasises about beating people up.
And I am proud to say I teach him these lessons first-hand, we often walk almost a km each way to get a bag or two of groceries and he has been doing that road march with me since he was four. He never again saw the interior of a stroller as soon as he could walk.
I find watching movies with kids is a great way to talk about various issues. I think people get too bent out of shape over questionable content. Kids walk away from 'lessons' having often learned very inadvertant things.