Goop

This is a fun and educational activity to do with children. Mix 2 parts cornstarch with about 1 part water. That's it. It's magic.
Sometimes it's solid,
sometimes it's liquid.
I don't fully understand it but it was really fun! Talk with your children about properties of liquids and solids -- and you could throw in gases too. Try squeezing the goop, pouring the goop...even just holding the goop is fascinating. I played right along with them for quite some time. They played for an hour. It washes off with water and is, of course, non-toxic. If you want to add color, add a drop or two of food coloring to the water before you mix it. It's really hard to mix in the color after you've put the cornstarch and water together.