If they monitor those kiddie porn sites then why haven’t they been shut down? The LEO’s monitor? How exactly - they watch them too??!!
I recall reading an article a few years ago where it was asserted that 99+% of child porn available on the internet was seeded by various police agencies as bait. There were a few known cases where an agency would take over porn sites (at least 18 months in one case) and run them as honey traps, sometimes even using the evidence locker to source new material. Then they would use porn ad brokers to seed CP thumbnail images into the targets' browser history and use that data in turn to open investigations, convict people, gain sentence enhancements, revoke parole, justify expenditures and budget requests, etc.
Interestingly when I tried to tried to search for the news articles about this, Papa Google threw up a warning that child porn is illegal and started censoring search results, apparently based on my browser fingerprint (I verified this by searching using a testing harness).