(My mom did this without the marble) .Making butter with a mason jar, heavy cream and a marble. Good project to keep the kids shaking while their main project is baking.then they can use the butter on toast!
I stumbled across "the spinning penny". I actually didn't believe this would work, and I sort of laughed at the warning Steve Spangler Science had put at the top of the page. "Warning: The spinning penny trick is known to be addicting".
Magic Milk Paint idea from Modern Parents Messy Kids. This is another one of those awesome 'science meets art' activities for children, and you only need milk, dishwash and food colouring to do it. Looks fun :)