A mixing bowl and spoon
1 cup of water
1 1/2 to 2 cups of cornstarch (adjust as needed)
Combine the cornstarch and water, along with the food coloring of your choice, in a mixing bowl. Stir until well combined. The stirring may be difficult at first, but it will become easier as your progress.
Oobleck is a real treat because it has the property of a solid and a liquid depending on how fast or slow your child pushes their finger into it.