I got this idea from this website and we had a lot of fun.
3 Cups of white flour
1 1/2 Cups of salt
1 1/2 Tablespoons of cream of tartar
3 1/4 Cups of water
6 Tablespoons of vegetable oil
Red food coloring
Mix the flour, salt, and cream of tartar in a medium saucepan.In a separate bowl, mix the liquids, adding drops of food coloring until you reach your desired shade. Pour the liquid over the dry ingredients and stir. Cook over medium-low heat, stirring constantly, until the mixture holds together and gets too stiff to stir (it will stiffen even more as it cools), about 5 to 10 minutes. Let it cool. Knead the clay briefly, then roll or pat it to a 3/4-inch thickness and cut with the cookie cutter.
I ended up cooking it a little fast and it got hard to stir quick, it was a little clumpy, but it all kneaded together beautifully. The kids loved playing with it. I will do this again. I used sandwich bags to place my hearts in and then yard to tie it shut. Have fun!