We have just about all of them on DVD and I like watching them especially when I'm not feeling bad. Even though she's just five, Emily's seen pretty much all of them. She loves the Hulk and tends to cry out, "HULK SMASH," when we watch The Avengers even when Hulk or Bruce Banner aren't on the screen.
When we saw the trailer for Guardians of the Galaxy, she instantly loved Rocket and wanted to see it. Even though she's only 5, we decided to take her to the theater when we saw it.
She was extremely excited - bouncing around as we waited in the long line to get tickets and then snacks. As the movie went on, she laughed a lot. She wasn't scared and honestly there wasn't of content that I thought was objectionable.
We saw it in a 2D show because while Emily will wear the 3D glasses she tends to want to take them off after a while. There were a lot of kids there - the theater was nearly full!
Marvel movies are really great family films - especially for a super hero lover like my daughter.