This stuff is really, really cool - it falls somewhere between a solid and a liquid, and passes back and forth between each state. It kept my daughter entertained for about 45 minutes, which is an eternity in toddler time.
2 parts cornstarch
1 part water
*I used 2/3 cornstarch and 1/3 cup water
Mix. Pour onto a flat pan and smoosh it around, make it drip, use cookie cutters, etc.