If they don't get the sex talk from their parents, they will get it somewhere else.
2. Gauge maturity. The talk you have with them depends on their emotional age. You definitely are not going to go into a detailed discussion about sexual intercourse with a kindergartner. However, you can have a chat about boundaries and private parts.
This is a necessary conversation for kids that are going out into the big world by themselves. As for teens, be prepared to talk about everything from blow jobs to anal sex because most of them are discussing these topics at school.
3. Open the door. Give them permission to come to you with any questions, comments, or thoughts. Open the door for communication.
If your kids know that they are not going to get in trouble if they come to talk with you about a tough topic, they will be more willing to come to you with their problems. Freak out after they leave the room.
4. Make the first move. Do not expect them to make the first move. Kids do not wake up thinking, "How can I connect to my parents today?" That's your job.
Go to them and open the discussion with, "Hey, I want to have the talk with you about sex. Let's chat tonight after dinner."