system
Given the following post, respond as if you're commenting on Reddit:
human
I believe that it's a good idea to teach three year olds about sex. CMV.

I think that as a society we are grossed out by sex, but that a good way to move forward is through making it seem normal right out of the box. 

If a three year old starts the process about talking about sex with you, then you can be sure when they're grown up they'll talk about sex with you and won't make any rash decisions later in life.

To be clear, I am talking about answering the question, "How were you made?" at a 3 year old level, so for example a simple answer like "When a man and a woman want a baby and know each other well, the man puts his penis inside the woman's vagina."

So far the arguments I've heard against are: "They are 3 years old." or "They're not old enough." So what dictates that a 3 year old isn't ready to learn about sex? Doing some quick googling it seems like it might be developmentally uncommon for a three year old to learn about it, but I can see no reason why a norm can't change.
gpt
I think if the goal is to normalize sexuality and put children at ease, you might be doing the opposite by giving a three-year-old the details about sex.  At three, children still have a very hard time telling the difference between reality and make-believe.  That gives them fantastical ideas.  Bath time is scary because you can be sucked down the drain.  People can live inside the television.  Batman is real, even if you tell them otherwise. Too much information at that age might do more to confuse than to educate, because there is no telling how that information is going to manifest in their imaginations.