To make Oobleck, combine 1/2 cup water with 1 cup cornstarch. Adding food coloring is optional. I've always found it interesting to play around with the amount of water and cornstarch while we play as well.
Tyler found Oobleck quite interesting, but wasn't sure he wanted to touch it. When he did try, he was much too unsure and ginger with his touch to dig in and scoop anything up as needed.
So I provided him with a wooden spoon and a measuring cup. He had much more success experimenting this way, and though he didn't want it on his hands, covering his feet with it was quite fun!
Ty was still able recognize the liquid/solid aspect of Oobleck, even without touching it. He was quite intrigued by the fact that he would pour the liquid into the dish, drop the cup into it, and the cup stayed on top rather than sinking in. He noticed as well that it looked like a liquid when in the dish, as it appears wet, but touching it with is hand gave him a different message.
As an extension to this play, there is a classic prose work by Dr. Seuss called Bartholomew and the Oobleck. In this Caldecott Honor book, a king who is bored with the everyday weather asks his royal magicians for a different kind of precipitation. What he gets is sticky green Oobleck falling from the sky, and hence, all over his kingdom! In the end, the king's Page, Bartholomew, then teaches the king a valuable social lesson...saying sorry. Highly recommended!