Here's a fun experiment you can do with simple ingredients from the grocery store. You'll need an adult to help, but the fun is all yours. And you'll learn some new things about evaporation, crystal formation, and the properties of minerals.
Making the Crystals
Put the water in the pot and bring to a bowl. Remove from the heat and place on a heat-safe surface.
Add the Epsom salts and mix to dissolve thoroughly.
Add a drop or two of food coloring.
Put the sponge in the small bowl. Pour the water and salt mixture over the sponge. Don't cover the sponge completely, or it will take a long time for the crystals to form.
Place the bowl on a sunny window sill, and wait for the water to evaporate. This may take several days. As the water evaporates, crystals will begin to form on the sponge.
TL;DR (Too Long; Didn't Read)
Note to parents: Epsom salts are non-toxic but they do have a laxative effect. Explain to your child that he or she should not eat them. Call your doctor if your child ingests a large amount.
Parental supervision is needed when using the stove and working with boiling water.