An example I like to make is of two girls age 8, who are found being sexual in bed. The parents decide to punish the girls, and separate them from future play dates. The parents are confused, and shocked, they perceive this behavior is wrong. This is very common.
It is important to know, however, that some peer exploration is common and is also often done with a peer of the same sex. Masturbation is also a natural part of sexual development. Punishment and shunning of these normal and natural behaviors may lead to shame and guilt about sexuality in adulthood and sexual confusion and embarrassment throughout developmet. (Parents should pay close attention to the nature of the exploration, as something that seems too adult or too advanced may indicate some inappropriate exposure to sexual material or worse, exploitation.)
When we are silent in response to sexual material brought up by children and/or teenagers, we mimic and reproduce the world the child is exposed to every day, one that excites and confuses him/her and provides them with little guidance or space for processing. As adults, it is important for us to take the lead and teach. Teaching children about appropriate time and place for masturbation is an example.
Here is the skinny, if we don't talk to our kids about sex, they're going to learn it anyway. And, Amy Lang, Children's Sex Educator and author of Birds+Bees+Kids, reminds us that by talking to them about sex gives us as adults the opportunity to instill our morals and values into the conversation, something they won't get from the TV or their peers. So, if you are feeling ill equipped, under informed, or worrisome about talking about sex, it is important to know that when we're silent that we're not providing assistance and that the teens aren't getting the adult help they need.
A trained psychotherapist in the area of sexuality can also be a great place to start.