Put on aprons and put newspaper out first! My boys love 'mixing potions': I give them each a bowl and let them choose what they want to put into the potion. I usually start them off with some vinegar and bicarbonate of soda for some fizzing action. I let them add mud, flour, food colouring etc etc they stir and pretend they are chefs/ wizards. Afterwards I encourage them to wash the bowls up themselves which generally creates even more mess