Although this is certainly an important topic, we have not yet addressed it in writing. We know of two relatively recent books on the topic: Talking About Intimacy and Sexuality: A Guide for Orthodox Jewish Parents, by Dr. Yocheved Debow (Ktav/OU Press, 2012), and Talking to Your Children About Intimacy: A Guide for Orthodox Jewish Parents, by Sara Diament (Xlibris, 2009). There is also much secular printed information available, but not everything that is written will feel comfortable for the observant family. The following are some common sense suggestions based on Dr. Zimmerman's experience as a pediatrician:
1) When children ask questions, they deserve answers. The answers should be geared to the child's age but should be factual. For example, when dealing with young child asking how babies get there one could say that a Mommy and Daddy hug is a special hug that only Mommies and Daddies can do. Older children can be told more information using the words for the body parts with which the family is comfortable. While many secular books recommend using the technical terms, some religious families may not be comfortable with using these words.
2) Children learn by example. Therefore, the more they see their parents being comfortable with each other, the more likely they are to feel the same way. Halachic parameters of modesty differ from those of secular society and it is not encouraged for couples to be openly sexual in front of other people. On the other hand, it is good for children to see that their parents are affectionate to one another. This can also be done with smiles or casual touch within the parameters of halacha and what the family feels comfortable with.
3) The more comfortable the parents are with the issues and the positive side of intimacy in the context of marriage, the easier it will be for them to pass this message to their children. We recommend the book Marital Intimacy by Rav Avraham Peretz Friedman for background reading for the parents (see English Books).
4) As far as timing, it's a good idea to try to find out what is standard in the children's peer group. Problems can arise if children are told significantly less than their friends already know, since they might end up getting inaccurate or distorted information from their peers rather than a more appropriately presented version from their parents. On the other hand – if you want your children to have more information than their friends' parents think is appropriate, the reverse problem can arise. Children should probably be told that this is a very private topic that should not be discussed with their friends. Though discussion and questions in the context of the home should be encouraged, stress should be put on modesty at the same time.