I found a great kitchen science project to do with the kids and I thought I would share it.
Pour heavy cream into a container with a lid. Have the kids shake the container until you can no longer hear the liquid sloshing around. At this point open it up and the kids can see that they have made whipped cream. Have a little taste, it's kinda bland without the sugar though. Put the lid back on and have the kids continue to shake the container. Do this until you get a thudding around in the container. At this point you will have made butter. The milk around it is buttermilk and can be used if you want, or discarded.
When I first read this I didn't think that it would really work, heck I am a city kid, butter comes in nice rectangular blocks that you buy at the store. The kids were kinda ambivalent about it at first, once we made the cream though they were excited to see the butter. The butter needed a little bit of salt added, but it tasted great on bread.