2 c. baking soda
1 c. cornstarch
1 1/2 c. water

Put in saucepan and mix. Heat on medium stirring constantly, until the mixture thickens. Turn onto a plate; cover with a moist paper towel and let it cool. The kids can knead it until it is of a consistency to mold. Shape into a form and put in a warm oven (250 degrees) to harden or let air dry for several days. To keep if fresh, put in an air-tight container.