I'm not protective of media exposure, so take this for what it's worth. I took both my daughters, 9 and 5. My 5 year old was bored about halfway through, and started running around in the theater.

My 9 year old really liked it, and she was the one who wanted to see it. My 5 year old sat still for Bolt and watched it beginning to end, but in general she is not a good one to take to movies. I'm not sure why I fell for her pleas again, but it's hard to leave one out of something fun like a movie.
Part of the problem was our movie was not in 3D. I didn't realize that until we got there, and my 9 year old was fine with that. The 5 year old still had her 3D glasses from Bolt, and I think she might have been more entranced had it been in 3D. Not in 3D the colors were muted and the picture wasn't as sharp. I was disappointed, and I'd almost like to see it again in 3D, but the story just didn't move me that much.