Here's a recipe if you want to make your own spray chalk:
6 tablespoons of Cornstarch
3 cups of water
10 drops of food coloring
Mix the ingredients in a bowl, then pour them in a spray bottle.
Spray the chalk on the sidewalk! To avoid clumping in the bottle, shake before using.
*Tip: Look for spray bottles at the dollar store or in the laundry section of Walmart.