By the way, here's how I dealt with the problem.
When the children were younger (say, 5: this would be the about 2001), I ran a filtering proxy at the edge of my home network. It contained a list of blocked URLs, and blocked terms in URLs and content, but more importantly it also logged all activity. I was pretty sceptical about the quality of the blocking, but I had the ability to see what each user of each machine had done, and I occasionally ran some reports on them. Adults bypassed this (you had to log on to the proxy) but the mechanism in use was reasonably secure. I think the basic policy was "if you're logged in as an adult, from one of the machines the kids don't use, and it's after the kids' bedtime, you pass straight through, otherwise we filter". That meant that if we were using the Internet we got the filtering if the kids were likely to be around, which seemed about right. With five year olds, over-blocking is benign: I don't care if some edge cases got blocked. As they got older, I relied more on the logging and less on the filtering.
The mechanism it used would survive a relative well-resourced attack by a computer science graduate for an hour or so, at least (I got my staff to tiger-team a similar set up at work) so I was pretty confident it would withstand the kids. It wouldn't block anyone with access to a VPN server, but with small children that's not a risk.
As the kids got towards teenage, we logged their activity, but didn't filter it. I had accounts on all the kids' machines, and I intermittently logged on and checked all was well (and could do so without them knowing, too, although I didn't do that). In fact we checked the logs a lot less than we said we did, but I did run a report on any URL which looked dubious, logged all videos that didn't come off youtube, and so on. I also had the means to log all internet access via the house Wifi from any device, although I usually left it turned off because it generated more data than was useful. Once a week or so I turned it on for a few hours and checked there was nothing untoward happening.
I think I turned most of it off when the kids were about fifteen. I still have the means to log all activity in the house if needs be, but it's sat there unused. The kids don't know that, so they self-police.
Plus the usual door usually left open, no secrets, I have accounts on all machines, etc.