Web usage - monitoring - keeping our children safe ...

I have two young children and would like to be more on top of their internet safety. Currently I have auto-forwards on their e-mails so I can see what they are receiving. The family computer is also located in the family room - so no closed doors there, but we also have a laptop and wi-fi enabled devices (ipods, etc.)

From a hardware perspective - it is all Mac. We have an airport extreme with an iMac, macbook pro, mini mac and ipod/iphones. I've been trying to look for software that will allow me to monitor web usage as well as social media (they are not yet old enough for that yet, but I'm thinking ahead).

I've only been able to really find one recommendation here - that was for Spector Pro, but was also written 2 years ago. Any suggestions on what the best approach is? I've looked into Spector Pro and it looks like a very nice package. I've also looked into Action Alert which also seems quite good but for quite a bit less.

I'm not concerned with the $ as long as it is worth it - I'm more concerned with affect on performance of the network. I've not seen any details regarding that for any of the packages I've looked into.

Any thoughts/suggestions are welcomed. Thanks!