Clergy Reporting Requirements

When a pastor learns of child abuse, what are his or her legal and ethical obligations to report the abuse to government agencies like Illinois’ DCFS?  On the one hand are the victim’s interests – those of the vulnerable child who has or who is suffering.  On the other hand are the interests of the confessing penitent, who usually receive assurances that their conversations with clergypersons are privileged.  Which interest prevails?  Which should prevail? What does the law require?