I find myself astonished again by what I read on a German message board - there they are having this discussion and the majority thinks that children should know about the technicalities of sex well before they are eight years old, preferably by the age of 4/5.
My dd1 is four and I find the thought of going into the details of what men and women do together a bit .
Am currently pregnant and dd1 has asked how the baby got inside my tummy, so we just said about daddy's seed and mummy's egg... then we changed the subject and dd1 seemed quite happy with that and I was glad that she didn't ask any more questions.
So, over to you...