In the name of entertaining things to do while cooped up in the house, we are trying some science experiments. The most recent (and I thought most impressive) was extracting DNA from an onion: you break down the onion's cells and, when poured into an alcohol-based solution, the strands of DNA combine into threads that you can see with just your naked eye. I heard about this one from one of my work chums who had successfully done it with his children: he sent me scans of the book he used but the gist of the experiment can also be found here.
Needless to say I think the girls were a bit underwhelmed with this one: not as good as the water rocket anyway. Plenty more stuff to try yet though!