The Avengers -
This movie went through fast, even though it's almost two and a half hours. The violence, isn't really that bad. It is fast-paced, but the worst thing that I can remember is Loki using some instrument to pluck someone's eyeball out (not shown). While that may be too much for a few kids, it is a very short scene and doesn't show any of it.
This is a fantastic movie that I think anyone 11+ could see, and while the violence continues, there are plenty of funny/stress relieving moments in it, and I believe your kid will enjoy it, if you let him enjoy it.
The worst language is d-mn, h-ll, and a-s. While the movie does have somewhat of a slow beginning, it picks up, and you find yourself enjoying yourself more and more.