To make it short and sweet "Our 4 year old son loved it." We had heard about the villain in the movie having yellow eyes scaring little ones, but as long as you view the trailers and talk about it ahead of time, there will be no surprises.
I felt like I was dragging my wife to this movie kicking and screaming, but 3/4 of the way through she said, "This is a good movie." I was shocked, she fell asleep in two of the Spiderman movies and yawned through Batman begins if that tells you anything.
This was a good role for Downey, it was also fun seeing Bridges in this light.