#1 is an understanding that children need to be able to ask parents about these things. They are going to get curious, they are going to look for answers. They will either look for it it from us, their friends, or google. As kids grow up, they become curious.

They will likely develop an issue with pornography at some point which I believe starts as a "curiosity". If there is a trusting relationship they will be more likely to turn to parents for help at some point. If a child understands that he/she can come to you with any questions or issues; you can help them before it becomes a serious addiction.

#2 I think it's a good idea to approach teenagers with "follow-up". Because they still might be too timid to ask you, but if you bring it up they might be more open to talking to you about it. I firmly believe it can be a very spiritually enlightening experience for both parties.