Tanya, I think that's a bit unrealistic.
Frankly, we have to realize that children today are exposed to sex at a very early age.
It would be best to be direct. Tell them about sex as thoroughly as possible and then tell them they should wait until they are ready to have sex.
Be sure to tell them about safety. That's the most important part.
And when they think that they are ready, or if you think that they have already gone that far, be sure to take them to see a physician about birth control and have that physician discuss the dangers involved in having sex.
It's better to give them the information that they need than to tell them "don't do it".
As far as growing up goes, tell them to enjoy childhood as long as they can because they will never get that time back. When they are older tell them not to spend their entire lives working and to enjoy life,find a career that they will always enjoy, and to marry someone that they love and that supports them and cherishes them.
Tell them to love as hard as they can even if it means getting their hearts broken because we need heartbreak to find the best of love. Tell them to never change who they are in order to get someone to love them because that is not true love.
Most of all, tell them that no matter what you will be there to pick them up when they fall.