Answers:
Why don't you only TALK to him/her? Communication is the best agency. Plus if you go through his/her room and be discovered, your child would never trust you again.
Think final when you become sexually alive do you really have an idea that you give bad "signs" that you be sexually helpful? Watch your child to see if they are interested in the contrasting sex. That is the first clue that it's heading some where on earth.
Well I dont know if you coulld really give an account. I believed when your child is more private going on for stuff. For example not letting you in their room, locking it adjectives times, and not conversation to you. If your child is a girl, you could inform by their body. The change on her body. Well specifically what some relatives vote.