Read Bartholomew and the Oobleck. For Kindergarten, it might be best to paraphrase the book, but they do "get" the message.
½ cup corn starch
½ cup water
green food coloring
Let the students help mix it/touch it. It looks like water when you mix it, but it turns to solid when you touch it.
Read The Cat In the Hat.
Make Cat in the Hat hats:
Give each student one piece of 18" x 12" white piece of construction paper and one piece of 18" x 6" red construction paper. Model how to cut strips of red paper and glue onto the white paper. Model how to leave space so it looks like stripes. Staple ½ a sentence to the top and to the bottom to fit around each student's head.