1/2 cup Elmer's glue
1/4 cup liquid starch
food coloring, if desired (1 drop for pastel, more for more intense color)
Mix in plastic storage bowl with hands. When mixture begins to clump, pick it up and knead and fold in your hands. Mixture will begin to soften, smooth and solidify as you work it.
This recipe made enough for my four oldest to enjoy a good sized dollop. I made it plain-colored, then added a drop of food coloring to each chunk so they could choose their own color. They just carefully folded the putty until the color was worked through.