Today with a friend we saw Monsters Vs. Aliens at a local theater as part of a spring free matinee promotion. The movie is currently available on DVD.
We enjoyed the movie. They had an intermission about half way through the movie which was nice to provide a bathroom break. However, it seemed like my daughter had a hard time getting back into the movie. Also, I felt like the initial setup was a little slow, especially for preschoolers.
Prior to seeing the movie, I had read reviews online about the appropriateness of the movie for young children including one that recommended it for children 7 and older. We still decided to go. I did not find the movie bad at all for my 4 year old. Of course, she regularly watches Scooby Doo & Star Wars: Clone Wars cartoons. There is some violence (it is a battle between Monsters and Aliens after all), but none of the heroes dies and even the villains are mostly bounced off screen (presumably to die). Actually during one scene, our kids found the the way the heroes were defeating the villains to be funny and were laughing at it. There was some very mild implication of sexuality/nudity. What was actually shown was very mild with an implication that went above the kids head.
Overall, this was a good movie that the kids enjoyed. I definitely recommend renting the DVD or otherwise seeing the movie.