Let the mother instruct a girl, the father a boy, and not leave so vital a matter to an unsuitable pamphlet.
Buy one of the many "Knowledge for Boys or Girls" books and read it carefully.
Having made sure you can convey a simple account of the wonders of reproduction, and that you have rooted out the idea that sex is something to be apologized for, see the child and tell him it is time he learned of his private parts, as manhood draws near.
Then, speaking in a quiet, unembarrassed way, deliver your little homily, all the time insisting on the marvel, the romance, the poetry and the beauty of the sex. Let chivalry be your text, not fear, and repeat the Squire's sound parting advice to Tom Brown:
"Never listen to or say things you would not have your mother or sister hear."
Give a clear and complete description in simple words of the mechanism and marvel of reproduction, for half-knowledge generates a prurient curiosity about the other sex, thus defeating the very end you have so earnestly striven for.
Purity not impurity should be your text, and you should only refer to masturbation as a harmful habit, which should not be contracted.
Warn them to
"Keep the heart with all diligence, for out of it are the issues of life!"
by turning their thoughts instantly and determinedly