Often parents have a lot of conflicted feelings on these subjects. It is important to identify your own feelings so you can clearly distinguish when you are discussing your feelings and when you are discussing facts when talking to your child. Children will pick up on mixed messages, so parents will do well to try to resolve their own conflicts. Sometimes I have had parents suggest to me that, since they have ambiguous feelings on the subject, perhaps it would be better not to talk about the subject with their child. These parents then run the risk of not being viewed as resources that the child can depend on in time of need.
Early discussions can be excellent practice ground.
The first goal is to create an atmosphere of trust and openness. It is not neceassary to include every detail. Children will understand and misunderstand information, but it is the feelings that leave a lasting impression. It is also OK for adults to acknowledge that it is not easy for them to talk about certain things as long as they also say they are glad the child asked and that they will try their best to answer. Just remember to label your own feelings as such rather than letting your child infer them, which can lead to erroneous and disturbing conclusions.