Oh I'm not denying that the author might have a questionable interest in young children, but the way the anime has adjusted things I think removes that for most viewers, especially those who are entirely unfamiliar with the original work or the author himself.
I don't know that I'd agree torturing the characters here, even if they are children, speaks to any kind of perverted interest (and I'm going entirely based off the anime here.) I think that's just part of the harrowing, upsetting atmosphere the entire series' wallows in.
Hell no. I don't think I've seen a show before that tried so hard to needlessly talk about a young boys penis so often when it was even almost entirely irrelevant to the story. Even if you were to argue that Riko and Reg might have several embarrassing run-ins, should those be actually relevant and be shown?
Scenes aren't thrown in randomly, they're supposed to serve a purpose. And at some point, you have to wonder if you haven't heard enough about Reg's dick or whether some half-nude shot of Riko was necessary, yet again.
Episode 13 shows some of vilest shit I've seen kids forced through in fiction. It follows that up with a heartbreaking death scene for one of those kids. And...not much later we this:
Because what else is more appropriate after enduring all that than talking about some young boy's erection!
It takes a special kind of perversion to put this in an episode with very detailed, horrifying children torture. And it really is so damn detailed that it's difficult to call it anything but gratuitous at some point. It helps tremendously that the episode was very well directed, but the actual content still feels like the author almost revels in coming up with some fucked up shit. If that weren't questionable enough, he contrasts that with his pedo shit every now and then. Great.
Honestly, if all that doesn't bother you. Fine. If you don't even see how even the average viewer could be bothered by any of this, then you're way deep into this stuff.