Who said there's nothing but junk on the Internet? I've made two great discoveries. The first is a website called the Khan Academy. It's a series of thousands of tutorials on just about anything you've ever wanted to know.
The other is a site that streams live web cams of various animals in the wild. It's great for all ages. Here's the link to it. Explore.com live cam.
There's plenty of other good stuff too but you have to be careful--especially if children are using the web. There's all too many ways to find yourself where you definitely don't want kids to be.