I'm underaged, but my parents really have no problem with letting me watch what I want to watch. Generally, though, I have very little desire to see films that are overly gratuitous, especially in the wanton violence department. ( I did, however, just watch
Dogma, which I found fantastically funny.)
As for little children... Well, my youngest brother was three in May, and this past month, my dad took him to see
Charlie and the Chocolate Factory while the rest of my family went to go see
Avenue Q. While my brother was terrified of the angry squirrels, he now goes around the house miming a pistol and screaming "Die! Die! Die!" He seems to identify with all of the "bad" characters (Darth Vader, Gaston...) and is definitely going through a gun and sword phase. I don't think that I would want to expose him to any more of it, if it can be helped, until he's old enough to understand what it means to be violent.
"'But do you really mean, sir,' said Peter, 'that there could be other worlds --all over the place, just round the corner-- like that?'
'Nothing is more probable,' said the Professor..."
-The Lion, the Witch, and the Wardrobe