You can either lock individual machines into safety mode (can be a pain for
many machines) or there are some firewalls that can force the lock for the
domain (easier). I'm not aware of an option in Google Apps to do this if your
school is enrolled.
Be aware that there is no such thing as safety mode for mobile devices yet
(iPads, iPhones, Android). Also note that the safety lock is browser independent.
You would have to enable the lock in each browser on each machine if you were
to do this manually. I suggest you speak with your current firewall manufacturer
to see if this capability has been added to your model of firewall. Otherwise I
would invest in one that does or perhaps find a software based firewall and put it
on a spare computer.