I think you have a false sense of security. I raised my kids with very little tv, no internet until they were in 3rd/4th grade and only one computer in the living room that they shared and was visible to all of us. No smartphones until they were well into high school, just some old flip phones that you basically could only make calls from. Despite that, my oldest daughter ended up in therapy when she was 13 and it came out that boys in her middle school (upper middle class, best in the area middle school) were harassing the girls with hardcore porn on their smartphones. She was so horrified and upset by what they were "shocking" the girls with that she ended up having sleeping and anxiety issues. She still to this day won't tell me exactly what she saw but her therapist said it sounded pretty bad (and of course she couldn't tell me specifics due to confidentiality).
But I agree that we should try our best. It doesn't mean they won't find it or it won't find them unfortunately.
I would feel weird policing my husband, but I'm sure you have your reasons. I would imagine it's fairly easy to circumvent the software through a VPN or TOR though, just so you know. In fact if someone were to attempt to do this to me I would just have a separate browser on a key drive and use a VPN. Trust me when I say, I would figure it out.