parents and kids

I think that there is a certain extent to which parents should 'spy' on their kids. First i dont think that they should spy on their kids at all. I think that they need to have an open enough relationship that they are able to talk to their children and be able to figure out whats going on in their lives and what they are doing. They should be able to trust their kids and believe that they are really doing what there doing. But on the other end of that, the children need to be able to earn their parents trust and not lie to them or give them a reason to 'spy' on them.
I believe that if a child fails to earn their parents trust, then it is nessecary for the adult to spy on their kid. To make sure that they are being safe. If it's for their own saftey, i think its nessecary, but if they are just doing it to be nosy, then i dont think it should be acceptable.