To help with citing sources, WorldCat has created EasyBib to help you cite webpages, books, newspaper or magazine articles and databases. This tool is especially useful to help you cite websites, which can be tricky. Copy and paste the URL into the search box and it will create the citation for you.
For middle schoolers, there is a bibliography site that list how to cite a work with examples, including encyclopedias.
When using databases, be sure to check the bottom of the article where you can often find "how to cite this information."