Aquard.io is an online fishtank. There are three webcameras allowing you to remotely view over fifty happy tropical fish through your web-browser. An arduino computer controls the backend allowing viewers to request feedings and squirt bubbles into the water.
If you want to teach the concept of The Internet of Things to children, then this is the site to come to. I showed this to three year 9 girls who are really into computers and they had to admit that it was 'quite cool,' however they wished that there was a chat feature. Presumably so you can chat to other viewers (not the fish). They also said that it 'wasn't fair' because somebody has 'bought a fishtank and now we look after it for free' (!).
You can join the fun on Twitter @aquardio.
A video explaining more.