A big box of corn starch, food coloring, several bowls, water, spoon
This is a fun and messy project for kids. Get out as many bowls as you want colors. Fill each bowl with a several heaping spoonfuls of corn starch, mix with a little water and food coloring. Keep adding water until it's soupy. If you let it sit even for a second it will start to harden, as soon as it gets moved with hands or spoon it liquefies again. Great tactile fun!