I looked at some of those videos. This is most likely an argorithm recommendation binge, that's why there's so many views on them but if you look at other videos of those channel they just have around 50-90 views.

Most of those channels are just kid upload the video themselves for their friends to watch, I know because my neighbour's kid also does it.

What really disturbing is the comments with timestamps, those are definitely pedophiles. And a few channel that you can tell is recorded by adult that just stay silent the whole time while the kid doing toy review in a bathtub.

Though I don't think there're 500k pedophiles on youtube, most maybe are just kids and normal people follow the recommendation binge. The easiest solution I can think of is to have the argorithm group those recommendation binge and have a human manually review them. It's unrealistic to reviews all videos but a strip of sexual suggestive (accidentally or on purpose) thumbnails take no time to recognize at all.

Or maybe make unlisted video the default option and call it "personal vblog" or something.