So be informal, spontaneous and leave the door open for further discussion. It is important to remember that you must provide the opportunity to talk alone with each child. Take every question asked at face value without jumping to conclusions. If you're sympathetic and the child trusts you, the chances are that she'll tell you. Let's talk it over another time.
Some parents are over-anxious about their children's' sexuality.
They want to know exactly how much their children know. You cannot insist a child tell you everything. This way sex gains dignity. So if your child asks you if you have intercourse you may reply, Yes, people who love each other normally do. If you are caught for an answer to a difficult question just say, That's interesting.