Depending on what you mean by "control" there are various options. If you control the router and secure it with password protection, you can use most routers to limit access, block domains, or disallow access during some time range or completely. You can also use QoS to regulate the bandwidth by connected computer or IP address on most routers.
You can also alter the hosts file on each machine to block all specific Internet sites that you want. It is located in Windows/System32/Drivers/etc, and can be modified using notepad -- any site you list in there will be blocked.
You could also use OpenDNS to configure what sites are available.