So last night we decided to chalkpaint the sidewalk. The paint is simple to make, cornstarch, water, and food coloring. There's no ratio of cornstarch to water, just put some cornstarch and food color into your container, I used a muffin tin, then add water and mix. My mixture was pretty wattery, which made it really easy to paint, but it took a while to dry.
You'll want a fair amount of food coloring, several drops, because the paint dries with an opaque chalky look, if you don't use enough coloring you won't have nice colors once the paint dries. It washes off easily and I don't think it will stain, but we decided that we don't care if it stains, because she's only this little once, so we might as well have fun!
Have fun painting!!