They did report it.
They told a family friend in law enforcement who never filed a formal report.
And they knew he never followed up, and they allowed the statute of limitations to run out.
When a report was finally filed, it was not by them, and they lawyered up to prevent the law from getting the full story.
Michelle and Jim Bob are accessories - they forced molested children to live with their molester and made sure he never faced the consequences.