Yes there is key logging software available for Windows, OSX, Linux etc. but it is a pretty invasive way to do things.
e.g.
http://www.spyarsenal.com/familykeylogger/
I keep our computer in the lounge room, all family computing occurs 'in the open'. But of course they could be connecting at school, the library etc. so I try to inform them of privacy and safety issues.
I personally left Facebook a few months ago and have been making more meaningful one-on-one connections with people since. It meant I have effectively lost contact with quite a few people as well, but I figured if they are unable to find the minute or two of time to keep in contact via phone, email etc. once a month or so, then they probably didn't quite qualify as 'friends' anymore. I miss it sometimes, but it was the right decision for me.
One thing to point out is that the data on Facebook never really goes away, and anyone of their friends can keep copies of it. It can hurt future job prospects, relationships etc. if all of the stupid stuff you say and do is recorded forever and is public.