Wikipedia is a free online encyclopedia created by its readers. While it has editors that can monitor the site and make corrections, it should not be used as an authoritative source. Before deciding to use Wikipedia as a resource for your students, you should take the time to discuss with your students how Wikipedia articles are created. There are several helpful pages within the encyclopedia which can help you work with the resource such as a page that explains how Wikipedia is created and a page that shows Recent Changes.
You might even consider having your class create or edit Wikipedia pages to give them a better idea of how entries are created! See Piotr Konieczny's article Wikis and Wikipedia as a teaching tool: Five years later