The advantages of being ranchers .... our boys pretty much grew up knowing the physical details (how babies get made, how they are born) just from being around the animals. We were pretty truthful from the beginning - used the real anatomy words and answered their questions when they asked. Bill was more uncomfortable with it all than I was ( maybe because I also have an anatomy/medical advantage ) so most of the discussions were done by me.
It wasn't until they were in the 7th-8th grade that we started discussing the "emotional" details.
With the animals around, the conversations just seemed to happen gradually and naturally. I don't envy you guys that have to come up with the conversation "starter".
Brenda - wife, mother, animal lover!
Canon Rebel T3i
Windows 7 & PSE 11