Great question! I have a great answer.
My mom was very depressed and repressed and wouldn't even talk about any of that. In fact, when I started my period she had the nerve to ask me if I knew what was going on...my snarky response was "yeah mom...from my friends, with no thanks to you.."
My dad took me aside after all this and have me these pearls of wisdom...
"Guys operate on the 4 F rule: Find 'em, Feel 'em, Fuck 'em, Forget 'em...remember that when they come sniffin around"....I've never forgotten it.

My mom, the very first time that I asked! (age five, I think). Her explanation was very clinical, complete with diagrams from a how-to sex book, and pictures from a Hustler magazine!

I got in all kinds of trouble (so did she) when I told other kids about it. I never understood why, when I was telling the truth and that their stork-delivery parents were flat out lying.

I’m not sure I ever had one. Learned in biology class.

I may have posted this before, if so my apologies.
Little Johnny has just turned 12 and his father called him aside and says he is going to tell him where babies come from.
Little johnny begins to sob, then cry a little louder and finally is wailing inconsolably.
His father asks him what is wrong.
Johnny replied,
"First you told me there was no tooth fairy"
"Then you said there was no Easter Bunny"
"Last month you said Santa wasn't real"
"and now you are going to tell me that adults don't really have sex, I have nothing to live for!"

My best friend in 6th grade. Her older brother told her. I tried to discuss it with my mother, but she pretended not to hear me.

My son was pretty young - I think six or so. He'd asked me about sex and I put him off. Later that week he asked me again. I was prepared. I pulled over the car and cautiously proceeded, trying to gauge just how much he wanted to know. Gave him a truthful but not too specific version. When I was done he sat there a moment, then said, "I'm never going to do that." He's 16 now. I am pretty sure he's changed his mind.