Currently messaging providers like WhatsApp and Facebook Messenger have an obligation to scan images against centralized hash databases of known child abuse ima

Currently messaging providers like WhatsApp and Facebook Messenger have an obligation to scan images against centralized hash databases of known child abuse imagery. End to end encryption unburdens the providers because they don't know what the message content is. This type of reporting catches people who are not just consumers, but are actively sharing and trading - in theory the people who might be directly abusing or trafficking children to produce content and may lead to organized rings. Given the direct evidence and the fact they find a ton more when they raid the house - they are slam dunk cases for the police. I don't have any hard numbers, but as you suggest I believe the vast majority of cases where they are communicating directly with children are self or parent reported. These cases of course wouldn't go away with end-to-end encryption.