I believe a responsible parent should introduce adult topics and issues to their children in a controlled and measured way to demistify them. It applies to sex, food and alcohol and many other things.
Introducing these topics early creates a healthy balanced approach in the young person's mind. Because it's not a dirty secret whispered behind closed doors it's not corrupted by misinformation.
This awesome book explains information and knowledge that everyone should have in an easy to understand way from a young age rather than getting it from an unknown source on the internet or shared between class fellows.
My recommendation is for parents to read it together with they children and have an open dialogue about this topic.
Please ignore the poor numpties who gave it a 1 star. Too many people still lived in the dark ages where sex is about guilt and shame. They prefer their kids to be touched by priests and for them to get pregnant before they even know about anything in life.