Theology of the Body and Humanae Vitae are a much needed area of catechesis for young people. But it’s important to do it the right way. Remember, the starting point is Jesus and our relationship with Him, not sex. There is a reason that the third pillar of the Catechism (the section on morality) starts out with the dignity of the human person rather than with a list of sins to avoid. We start with the affirmation of the good rather than the pointing out of the bad (else we don’t know why it’s bad).
The reason that fornication, masturbation, pornography, etc. are sins is because of our great dignity as human beings made in the image and likeness of God. It is extremely important to get across the truth of our human dignity and its relationship with morality, else all of Catholic sexual morality will not make sense. It will only seem like arbitrary rules meant to keep us from having fun.
Just something to keep in mind.
Edit: Even Scripture begins with the good and the dignity of the human person (the whole “created good and created in God’s image and likeness” comes from Genesis 1). The Fall comes soon after, but it is not the very first thing. And even with the Fall, there is immediately a promise of redemption (Genesis 3:15).
