Sparrow,
I think the admittance of guilt even after an accusation is a confession and protected. A confession is the unburdening of a transgression or wrongdoing. There is no condition about when the information is confessed.This is privileged information.
A child reporting abuse is approaching the adult authority figures in their lives for assistance and protection. This is not privileged information.
I don't understand how regular adults can sleep at night knowing that a child has been abused and feel no responsibility to report it to the police no matter their standing as a mandatory reporter. We should all consider ourselves mandatory reporters when it comes to children, or vulnerable others.