No act/victim, no report. One can't be charged for thoughts, only behaviors. And, unless the reporter knows who the child is, there is no way to report to child protective services. If I had a client who said they sexually abused a child but I didn't know who the child was, I can't report anything.
It's probably different in matters of national security ("I'm going to blow up a school") in that the police would be interested in an unknown victim(s) to prevent a crime but it can't be done with "So-and-so is suspected (or admitted) to abusing a child" whose identity is not known.