I personally think spying on your children is a losing propostion. If they don't feel that they can confide in you now, how will they feel after they find out your spying on them?
They will find out. If they are computer savvy, they will eventually detect it or you will confront them with something you found while snooping. Here is a pretty good
article detailing the problems and consequences of spying on your children. How would you feel if your boss, spouse, children, etc... were spying on you? I am sure they could come up with a lot of valid reasons why they were doing it. "I wanted to make sure he/she wasn't stealing from me" or "I wanted to make sure he/she wasn't cheating on me" or "I wanted to make sure my parents weren't spying on me."
Also, a lot of keylogger and spyware vendors are not the most reputable companies in the world. Be careful that you aren't the one that is getting spied upon. I have written an article on
spyware that you may find helpful.
Good luck!