Sky-Map

Sky-Map is a great site with information on all things space-related - astronomy, astrophysics, and so on.  It's a graphical site that lets you click on different sections of the sky and learn more about the different formations, bodies, and history of that area.  The site also offers a lot of information on different space-related phenomenon, largely articles supplemented with a huge quantity of quality images.  The site only covers items outside of our solar system, so be aware that it's not going to help with your kid's project on Pluto.  Hopefully that will be an omission that the site soon corrects.