I never had "the talk" and was educated by the Internet about that subject, like most things.
I'd agree it's important, and it helps protect them, but it can also hurt them if you lie to them about it. I find it best to simply tell the child honestly what sex is and why people do it, and to clarify with them why they probably shouldn't have it, being that being a child if they had sex the other person could go to jail for YEARS because it's illegal because they want to make sure kids aren't hurt (ha as if that's why!), and that it can be dangerous if it's not done correctly and with someone who loves you and you love them in a dating type of way.

Sounds odd, but I believe in treating kids as equals, and that's the facts. If they want to have sex with their hand (masturbate) every night, even relatively inappropriately in the same bed as me, that's fine, well, maybe not the latter.
It feels good to them and it's not harming anybody or traumatizing them.

But if they want to have sex with somebody else, which oddly enough does happen especially with the lower starting of puberty and more knowledge available to them as true pre-pubescences, they should know the actual risks, not the fear-mongering lies and fear-mongering, but the genuine real deal.
Don't talk down to them, simply explain to them how it is and advise them not to engage in it for rational reasons and they'll listen if they have any faith in you as a parent.
If a kid does happen to want to try that with someone they won't want to put them in Jail, and if they don't want to try it and sometimes forces them to, they will know their options on how to get rid of the person as well as likely to prevent the situation entirely.

But again it's all built on trust, between you and your baby. If they don't trust what you say and genuinely care about how you feel anything you say is meaningless.
If you lie to them about sex, even a little, when someone tells them otherwise who they may trust more, they'll defy your wishes and do what pleases them,for example if you said "it's only for adults" they may hear otherwise from other kids, then when an adult attempts something with them they had no reason to decline as they do not understand the implications or potential results of the act.

A child's innocence is not their lack of ignorance, it's the lack of disgusting depravity the've dealt with. They can know all about sex but that won't take their true innocence and carefree behavior away.
What steals that is not education but destructive behavior, be it by them or by another, be it regular violence, emotional abuse, or something forcibly raping them. That's what destroys innocence; it's the thing that you lose when you lose faith in others and begin to feel alone.

EDIT: Oh god I Story'd your story I did it again, I really should try to make these posts more subtle and simply make my own post for when I let my hands go'a'typin'