A proxy would require me to change the browser settings to use the proxy, right? That is how I am doing it now but all my kids have to do to get around it is change the proxy settings to not use it. I was hoping to hook a bit lower into the NIC so I could watch any browser request.
Set up a redirect rule on your firewall for all traffic coming from that IP address intended for port 80 on a remote machine to pass first through a proxy on the firewall. This requires a NAT box with filter rules you can control.