Just because a belief is popularly held for a long time and passed down through generations does not make it true. This is one of the most common fallacies*. That is the reason so many people are critical of beliefs that are backed up with religion. If you believe something strongly, you really need to be able to back it up with reasons. Tell us why you say it's wrong--not just that your parents believed it, so you believe it too.
*EDIT: Actually, it's a combination of three informal fallacies: 1. Appeal to Tradition, 2. Appeal to the Masses, 3. Appeal to Authority