A little known fact: babies begin masturbating to the point of orgasm while they are in utero - still in the womb! Our cultural insistence to see children as asexual is a form of denial which creates a lot of damage.
As an incest survivor, I am well acquainted with how debilitating adult/child sexual interaction is. I am adamantly opposed to anything which removes the incest taboo for a variety of reasons and I understand how fearful we as a society have become about child molestation. It is a very real problem and the damage it creates reverberates into society leaving mental illness, addiction, alcoholism, domestic violence, rage and suicide in its wake.
In the seventies and eighties we fell out of our mass delusions about how trustworthy priests, rabbis, pastors, parents, teachers and other adults in positions of authority really were and that freed us to examine the truth about child molestation. Laws were enacted to protect children from adult sexual contact. As someone who was not protected as a child I have a deep appreciation for efforts to protect children.
But swinging to the other extreme where we are afraid to even acknowledge that children think about and experiment with sex isn't healthy. It communicates sexual shame which can cripple the sexuality of children so that they find it difficult to function when they become adults.
I believe sex education should begin at the earliest age possible. It should occur in stages so that the child is never introduced to information they have no interest in. This will vary from child to child. There is no specific age when certain information should be dispensed. Rather there are varying levels of curiosity which should be satiated in a shame free context.
Each child deserves matter of fact answers to any and all questions about sex which they may pose. And every child absolutely needs to know that the adults in their world will provide the information without burdening them with personal details about their own sex life. This is called a boundary and one should have healthy boundaries when communicating with children about sex.
Create a caring, safe space where the child navigates the conversation to the points which interest them at any particular moment. Remain open to further inquiries out of the blue as questions and curiosities about sex will naturally arise as the child ages. Learn to answer those questions without fear or judgment.
The one thing I would absolutely include in sex education for children? This:
Sex is an extremely important part of being alive on planet earth and it is meant to bring us joy, creativity and our connection to the Divine. Sharing sex with another human is best delayed until one is an adult but please have sex with yourself often and learn to incorporate it into your spiritual and health practices.