Yup. This.
In which ways do you think it is underfunded?
CPS should be able to spot children in abusive homes and respond to reports of unusual activity. They should be able to spot clearly unstable caretakers.
Counsellors and teachers should be able to spot unusual behaviour from children. Mental health services can help someone escape falling into such a situation in the first place by keeping them from falling into depression which leads them to rely on such a person.
Local police shouldn't dismiss leads so readily. This is the it is impossible for him or her to do such a thing mindset which prevails so frequently.
Parents shouldn't trust their relatives so readily and should keep an eye out. 90% of cases happen at home.
If they stopped showing off their crimes online, would the entire system come to a crawl? I'm worried by how much of a reliance there is on divining crimes off the internet.
My personal political answer to "how to have end-to-end encryption and prevent its use for child rape" would be to tax the companies which profit from E2EE, and use that money to fund death squads, which livestream dragging child rapists out of their home, anywhere in the world, and beating them to death with truncheons.
I'm joking, of course (or am I?) but I do consider this the general shape of a viable solution. E2EE is essential for a modern life which isn't a hellish surveillance dystopia, and the detection and prosecution of child rape is criminally underfunded.