Trio
For us? The talk isn't just ONE talk, it's a conversation that happens over time and situations...it's important for people to know the CORRECT names of body parts. It really helps in picking up cues from kids and their conversations.
We have allowed the school to "inform" the kids, but we ALWAYS ask questions. There have been some W. stories told (i have a freshman in high school) and we've corrected those.
When situations present themselves? We have a talk. We ask questions, state our beliefs, morals, values, etc. For example, when our kids were younger? We LOVED (well, I still do) the Magic School bus. We have a book about farts. Yep! A book about farts - we have two boys - and while I would prefer the term Passing Gas? Yeah - my boys LOVE "FART". That book was GREAT when they were 4 and 5 years old - as it showed how the body worked at THEIR AGE level.
Now that they are 12 and 14? We have two Human Anatomy (one is the Encyclopedia of the Human body - it's HUGE and has EVERYTHING in it) and the other is a small book, more like a pocket reader, on the Human body) books in the bathroom that we use mainly during the day. They ask questions - we answer. It's NOT ONE conversation or talk! You keep it moving and going! Keeping the lines of communication open is the best way. LISTENING to your kids when they talk.
Good luck!