I met one student who was involved in cyber porn. His parents had no clue what he was doing on the computer. They knew there was a change in his life, but they didn't know why. He came to a camp and we had to pray for deliverance in his life. Parents need to invite their friends over for a night at the house and see how they talk and interact.
Communication clearly exposes what's in the heart.
But God has called us to do that. It's our right to walk into their room and lift their mattress to see if there are any ungodly magazines there. It's a God-given right while they are in our home. My mom always told me that while I was in her house, I had to abide by her rules. She found things in my room at times when I wasn't serving God.