We run a kids website at http://mocomi.com/ which offers free educational lessons to kids. We also have a lot of articles, videos and worksheets on our site for kids in a wide array of topics. You can check them out here: http://mocomi.com/learn/, I'm sure you'll like them.
You can also check the other categories out here:
Science: http://mocomi.com/learn/science/
Physics: http://mocomi.com/learn/science/physics/
Chemistry: http://mocomi.com/learn/science/chemistry/
Biology: http://mocomi.com/learn/science/biology/