In a large bowl stir together baking soda, Epsom salts, citric acid, and cornstarch until all ingredients are well combined.
Add coconut oil and essential oils. Stir well again.
Mix in your food coloring if you opt to use any until you get your desired shade.
Now you are going to add the water, just a couple drops at a time and mix it up with your hands so that you can feel it. You want to add water and mix just until the dry ingredients are lightly damp and if you squeeze them they lightly hold the shape.
Press firmly into one side of your mold, press in a small toy. Some items that work great are little mini-figures, bouncy balls, game pieces, and Barbie accessories.
Fill the other half until it overflows a bit, press the two halves together, you want to make sure that there are no air pockets and that the mixtures squish out the sides a bit when you press them together.
Allow to dry for 3-4 hours or overnight then carefully remove the molds.