One reason for sexual purity is to avoid AIDS, herpes and other dreaded diseases. Fornication causes emotional wounds, troubles in marriages. Think of the shame that accompanies unfaithfulness to one's husband or wife and that comes with premarital sex. But for the Christian, the main reason is that Jesus Christ forbids it. This grieves the spiritually minded Christian.
Parents ought to teach children to fear fornication as they fear any imaginary monster.
Their children must know about the deceit of fornication, the allure of fornication, the power of fornication, the destruction of it. The children don't learn this by listening to what most have to say today. Even advertisements on most innocent and profitable programs are sexually oriented, so that the children's opinions about sex are warped. The children don't learn this by listening to most music on commercial radio today. Most of rock music's lyrics as well as its beat are designed to arouse the sexual passions.