Often when I was doing my IGs, I would not know about the contents of a movie until I had actually watched it, or had heard what my friends had to say. Often, these movies have a lot of nasty scenes in them, that you really do not want to watch, and often what seems like a decent movie will turn out to be the opposite.
To solve this problem, IMDB (Internet Movie Database) has made a very useful page for every movie called the 'Parent's Guide'. The parent's guide can be found in 'Additional Details' section.
For example, you want to know if there is anything inappropriate for your little brother or sister in a movie, here is what the Parent's guide would look like for Iron Man 2.
Enjoy whatever movie you want to watch now in peace!