Thanks nothing2lose - From what I've also read online (and yes I know that not everything is to be believed online) it is fine to introduce these concepts at four but no need to go into every little detail at this age, more because of the fact that they have low attention spans. I've been reading articles written by child psychologists, so I am tending to trust what they are saying. Some are saying slightly different things on how much detail to go into, but they all agree that it is appropriate to introduce sex education at age 4, just no need to go into every detail. I might also talk to some child psychologists to make sure the information is correct though.
Just saw your response myturn - and from what I'm reading what you've said is what child psychologists are saying. :)

