This government site provides information on the CIPA law and its applications to schools.
"The Children's Internet Protection Act (CIPA) was enacted by Congress in 2000 to address concerns about children's access to obscene or harmful content over the Internet."
This government site has free resources for teaching digital citizenship. You can order free education booklets and other materials for your whole school. Make sure you scan these materials before giving them directly to students, especially at the elementary level. Some materials contain mature content and should be delivered directly to parents, perhaps during conferences.
"The Net Cetera online toolkit offers free resources to help you teach people in your community about kids' online safety. Regardless of your experience as a speaker - or your expertise in online safety - this kit has the resources and information you need to convey key points about protecting kids online."