This project was a Pinterest success and one that entertained the girls longer than 5 minutes!  I pinned a couple variations of this sidewalk chalk here.  This is the recipe I thought worked perfectly (and was easiest to make):

We used old paint brushes and painted on the driveway and also filled a few spray bottles and sprayed the chalk.  Both worked great.  The mixture dried quickly into a colorful, chalky texture.  It came off the driveway easily with water.. bonus!

Of course, they had to try painting their arms and legs too….