If they're not taught properly at a young age, they'll learn incorrectly from their friends.
You need proper education. Sex is all around us, there is no way to shield a child of around 9 or so from learning the term "sex.". Children are naturally curious, and that should never be discouraged. They should know about the world around them.
Do I think you should be discriptive when a child is 7? Hell no, but at the same time they should learn proper termonology for body parts.
But proper education should never be discouraged. They will find out the information one way or another, and it's better they recieve the correct info.
Now truly, goodnight.