Jobo84 and Shakira
Telling children (or letting them believe) that people only have sex because they want to have a baby is a fictional account. It is not a simplified or less detailed version, it is just not true.
I remember learning about sex and thinking - OMG that is disgusting and weird etc...my mum and dad must have done it twice, the Queen and Prince Phillip must have done it four times etc... but then I asked some more questions and got some honest answers.
Do you really tell your children po facedly that you've only ever had sex with their father, and only when you were trying to conceive, that it wasn't pleasant or enjoyable, but you got it over with because you wanted to have children. Or do you just not talk about it and let them think work out that is what must have happened (it makes logical sense, and kids are very logical...).
How do you talk about contraception, if people only ever have sex when they are TTC? How do you tell them that someone might want to touch them or be touched by them, and they can say no and they can tell other people (because logically it wouldn't happen because people only do that when they are TTC in the version you are leading them to believe).
You can tell children that sex is important, has consequences but is also fun.
Whatever age your children start having sex, they will do it because its fun. (You hare not you really hoping that your children don't have sex until the day they start TTC, surely?) You hope that when they start they will do it responsibly and when they are emotionally ready, and you hope they will talk to you about it, if they need information, or help working out conflicting feelings about this. But how can they talk to you about it if you have told them that sex is not something you do for fun?
Shakira - a parent has the right to tell a child any old nonsense, that the liver pumps blood, that nitrogen is used in respiration or that other races are inferior or whatever, that is their prerogative as a parent. But a child has a right to learn accurate, age appropriate information at school.