Combine the baking soda, sugar, cornstarch, and cream of tartar in a mixing bowl and stir well.
If you want colored kinetic sand, mix a few drops of food coloring into the water in a separate bowl.
Add 2 tablespoons of water to your dry ingredients and mix.
Knead with hands and mix thoroughly.
Test the texture: Too dry, add a little more water. Too sticky, sprinkle in a bit more cornstarch.
Let them play!