Barracuda, iPrism.
As an FYI, the problem with such a filter is that your children can simply disconnect it and reconnect the unfiltered internet.
This type of filter can usually be setup to send an alert email if it detects tampering. Also they can either be setup as fail-safe or fail-secure. In fail-safe mode all traffic is unfiltered if the filter is offline, in fail-secure mode all traffic is blocked.