You will want to disclose this and get it professionally cleaned. Put yourself in the buyer's shoes. You would want to know when and where the mold was, photos to document, and a receipt/remediation assessment from the vendor who cleaned it. Doing all this could prevent a costly lawsuit later on.
Serve Pro can come out and give you a free estimate and make a recommendation. They help homeowners and businesses with this problem. They give great advice. This link will take you to an interview that explains more. And by the way, Chlorox does not kill all mold. That's a myth. Check out this link for more info. http://youtu.be/Gm-ywAzjkaA
Yes first of all even if you are aware of the mold in your house you need to by law for sure. You can get a mold remediation done by a professional or can also get that dry wall replaced. Generally what do is cover all the walls and scrape it. Google how it's done and you'll know what I'm talking. A lesson for life is disclosing all the facts, a stitch at time saves nine...
Please read this Guide to Mold and Moisture in Your Home published by the EPA. http://www.epa.gov/mold/moldguide.html It includes advice on who should clean up the mold, and when the homewoner can do the job themselves. If your situation is one that meets the do it yourself recommendation, this guide offers a "Do It Yourself" guidelines to follow. :-)
Click on the link and read the EPA's recommendations. you will be okay if you folow the guidelines in this publicaton.