OpenWRT has prometheus node exporter packages. But in your case I think a PiHole would make sense, first of all you don't need to put it on the router, just po

OpenWRT has prometheus node exporter packages. But in your case I think a PiHole would make sense, first of all you don't need to put it on the router, just point the router's default DNS to your pihole. But a pihole will give you a nice dashboard of all the DNS records resolved in your network. Which will give you a really good idea of what your kids are doing, since most of it is via DNS.