What do you believe your responsibility is as a teacher when using content from the web in yor class

In the past I have mostly used educational sites like NLVM and other sited designed for use by students. I occasionally use clip art/pictures to add to notices etc. but I find these under images and can only use the free ones. I rarely use music but am guilty of occasionally getting songs. I more often load cd's into my music library. I believe that it is my responsibility to inform students but at the grade 3 level, parental control is more prevalent. It is not really an issue in my classroom.