Lying to kids will produce liars when they are grown up. But certain things are indeed hard to talk about.
If you want to be able to talk to your children comfortably about sex, what you really need to do is make sure you are comfortable talking about it, first of all.
We have trouble talking about sex to kids because we adults have created these walls in our head about sex. There’s daily human life–eating, drinking, working, sleeping, going out, watching a movie, playing sports–and then there’s SEX! And that’s a whole different animal.
Actually… no, it really isn’t. Sex is simply another natural human activity. Yes, sex done improperly can have bad consequences, but so can cooking, where you use sharp knives that could easily stab someone and flames/ovens that could badly burn someone. And then there are the electric gadgets we sometimes use. Done properly, cooking is enjoyable and no one gets hurt. Same thing with sex.
This is not to say that there is no difference… there sure is. Sex is the most intimate of these activities. But even then there is no great wall between sex and cooking, any more than there is a wall between meditative yoga and shaving. Yet we put absolutely no shame on yoga, cooking, or shaving… that is, unless said activities involve a sexual part of the body.
These is all this taboo and shame regarding sex. But sex should not be shamed at all, it should be celebrated. Why put shame on something so beautiful? Well, there are many reasons why, but still… all this shame and hiding only messes us up later. They’re always telling parents: talk to your kids about sex–before they learn the wrong things on their own. Because eventually, they will learn. Sooner than you think.
So don’t be afraid: the little that a child might know about sex is not even thought of as “sex,” let alone this thing totally apart from the rest of our lives. Kids are much more pure of these dirty thoughts and don’t make the associations that most adults make, sexualizing things whose character is far broader and richer than just its sexual element.
When a child asks about sex or something to do with sex, it is an innocent curiosity, just like when [s]he might ask you about what you do at work. If a child does get really specific about sex acts and things like that, you really do need to engage with them anyway, because they’re already learning this stuff somewhere else and are likely to get a lot of misinformation about it. If the questions continue, especially if the child is pre-pubescent, then you might have a more serious problem—sexual abuse. And then you will really want to talk to them about it.
But talking about sex correctly with children is a good idea anyway—the less they see sex as this forbidden thing never to be talked about, the more they will be able to talk about it, and the better their defenses will be against the sexualized garbage put out by the media and popular culture. This business of sex as a dirty, taboo thing is further encouraged by the media presentation of it as something to be objectified and sell products with.
Remember—sex is not about all this trashy, “sinful” balderdash. We love good sex because it feels good—that’s not a bad thing! Because we enjoy its intensity. Because it’s therapeutic. And in that word, therapeutic, you have the germ of a nice, neutral way of describing sex without taboos: physical therapy. Nothing at all wrong with that, is there? And best of all, it’s totally true! So now you can talk about sex to your kid on those occasions when you need to without ever breaking a taboo.
EDIT: a friend of mine adds this: It is important, though you may talk about sex as physical therapy, not to hide from the word “sex.” This I do agree with. It’s a question of changing the dialogue from “sex as forbidden subject” to “sex as an adult way of sharing love,” being very clear about the “adult” part.