You can buy chalk at almost any department store such as Walmart, Kmart, Walgreens, Target, Rite Aid, CVS etc...If you are ambitious you can even try making your own chalk.
MAKE YOUR OWN CHALK
Then find your canvas (a nice clean side walk) and draw your masterpiece. Let your imagination soar and have fun.
Now some special tips for your Mommy and Daddy--Here's some household tips for those little pieces of left over chalk.
1. The next time you have a grease stain or a little ring around the collar, grab some chalk. Rub it into the stain, let it sit for a few minutes, dust it off and launder as usual. The chalk dust will get into the fibers and absorb the oils that are causing the stain.
2. Wrap a small bundle of chalk in cheesecloth, tie it off and store it with your silver to keep the pieces from tarnishing. The chalk will absorb excess moisture, which can speed up the tarnishing process.
3. This same method will work in your toolbox to keep your tools from rusting.
4. Put a bundle in your closets and cabinets to keep them from getting damp and musty.
5. The next time you need to trace a pattern on something, use chalk. It will be clear and easy to see and you can simply dust away the lines when you're finished with your project.
6. To keep ants out of your house draw chalk lines around your doorways and windowsills, ants won't cross over the line.
Credit for household tips:http://simplymrsfixit.blogspot.com/2011/03/alternative-uses-for-chalk.html