Another really fun and messy (and cheep) activity is oobleck. This is literally as simple as corn starch and water but it has an amazing property of behaving like both a solid and a liquid. If you try to punch or poke quickly through it, it acts like a solid, but slowly slide your hand into it, and its like water.
2 cups cornstarch
1 cup water
Food coloring if desired, but could stain hand or clothes
Riley got in on the action, and I adore this sequence of pictures of his exploration:
He tried to eat it. Decided it didn’t taste good, but it didn’t seem to matter. He kept trying to eat it again and again.
Because it’s corn starch and water, it cleans up really easy! Just some warm water. Landon loved playing with this. I have to admit it’s pretty fun for adults too (just use the excuse that your child wants you to play with them then you’re covered!)