This is a little game that might be a good intro to a lesson on 3D visualization for kids.
Here are a collection of videos that in simple language explain aspects of computer technology including blogs, twitter, wikis and more.
This site has organized over a thousand videos that kids can learn from. In particular they have a category for computers.
This page has some awesome 3D fractals. Some videos too.
An explanation of how they are created is given on http://www.skytopia.com/project/fractal/2mandelbulb.html
If you want to give some perspective on the history of the Internet, this is a very good page for some info on that.
Here is a nice basic intro to how the Internet works. The presenter, Marti Hearst, is a professor at Cal Berkeley. The material should be suitable for high schoolers. The slides are also available http://www2.sims.berkeley.edu/courses/is141/f05/lectures/se-course-intro.pdf