I'll be interested to hear this as well. Seems a bit of a minefield. I remember on my previous ISP (TalkTalk) you can basically restrict adult content at an account level (possibly via DNS) but that is rather restrictive.
On my new ISP (Gigaclear) I'm not sure they offer the same sort of thing even though I thought this was a requirement for the ISPs a few years back.. the only suggestions I can see with them is to block certain websites by device on the router... A whopping ten sites! Crock of shite that is. Interestingly there is a block by category that may be more useful on the FAQ documentation but that seems to be absent on my router firmware.
I've never looked into it but there may be software out there that can be installed onto phones, tablets, PCs etc that has great blocklists of sites that it will stop people getting onto. Only problem with per device blocking is if they sneak another device into the house. Although this could be monitored on your router and it's internet access fully blocked if you did suspect that was happening.
