Liquid starch
Rock salt
Glue with food coloring
Spoons
Bowls
Cardboard

Mixture: Mix 1/2 cup liquid starch with 2 cups rock salt, 1/2 cup glue, plus food coloring or tempera. This makes a gooey, rocky mixture.

Let the children freely pile onto cardboard to create a three dimensional structure. These will crystalize and dry hard.