This is a topic that can go on forever and ever. In college, there are entire four credit classes dedicated to study this topic, particularly for future healthcare workers.
Teach children that sexuality needs to be safe.
Teach children that sexuality is good and healthy as designed by God.
Teach children that when we break God's laws, we hurt someone else and our future. Dishonesty is harmful.
Teach children that self-control is key to happy healthy sexuality. Including the ability to not 'lust' after pornographic images and webpages.
Teach children that we should not touch a person whom we are not betrothed to or married to in a 'special way'
Teach children that we should use and read the bible daily to help us love our first spouse.
These topics of conversation can start at age eight and go on until the child has reached marriage. Before age eigĥt, teach general safety and where adults or other should not touch.
(early conversations to help children understand sexuality topics) http://www.intoxicatedonlife.com/2015/10/15/christians-stop-protecting-your-kids-from-sex/
(video: sex has a price-tag)
***modesty and apostolic importance** http://www.acpublications.org/Marriage-and-the-Family.html
www.sonlighteducation.com (helps the younger child understand that we are a part of natural orders) includes very good illustrations of animal behaviours and illustration of reproduction of plants and the holy nature of God.
(unassissted childbirth: reflect exodus 1-2 about value of childbirth) http://www.amazon.com/gp/product/1499152035/sr=8-8/qid=1455593370/ref=olp_product_details?ie=UTF8&me&qid=1455593370&sr=8-8
(all things midwifery) http://birthjunkie.com/book-product-recommendations/
(talk about polygyny or different types of sexuality) http://www.beliefnet.com/faiths/2001/02/polygamy-not-as-rare-as-you-may-think.aspx
further article: http://www.intoxicatedonlife.com/2016/09/05/what-we-wish-our-parents-would-have-taught-us-about-sex-as-teen/#
**talks about modest religious groups** that do not embrace God's laws example: muslims, hindus, and so forth.
When the child has reached betrothal and marriage age, they may read the book 'intended for pleasure' by Ed Wheat. But do not read the book until then, as it could spark too much curiosity where it is not needed.
All in all, a child should not be practicing sexual things until they can build and live in their own home.