In this time period Germany was still deeply religious. 95% of the population identified as some sort of Christian denomination, whether it be Protestant or catholic. The Nazis had worked to try and reduce the Christian influence on society but they hadn't succeeded and as such there was a clear parallel in education between those who took to the Nazi teachings and those who subscribed to the older Christian conservative way of thinking.

Now both methods praised the role of motherhood and encouraged procreation within the bonds of marriage. Where they split however, is in the racial purity doctrine and the ultimate goal of sex.

The Nazis stated that sex should not be for pleasure but as a means to serve the state and raise a large family of Aryan children. It was also looked at as a means to control society. Women and men were taught about perverse acts like homosexuality but they were told that they were immoral and a result of corrupt Jewish influences. There were set beauty standards for women and men. The boys and girls would have been taught to conform to traditional German images and the Nazis even set standards for how women could be portrayed on art so as to show the young girls how to act.

As for the racial policy I mention above. Well as the war went on and more and more men were killed hitler realized he might not have enough future Aryans to inhabit his reich. So women and young girls in schools and in the league of German girls were taught to have pre-marital relations with Aryan men for the purpose of having as many children as possible. Himmler even went as far as to endorses polygamy of sorts of it increased the amount of children.

Back to your original question about what would a 16 year old boy and 16 year old girl have known about sex? Not much scientifically speaking, but they would have understood their role and would have been encouraged to have sex by the nazis, while being told to remain chase by their church and elders.

Sources:

Third reich at war : Richard Evans

Third reich in power: Richard Evans

https://ejournals.library.ualberta.ca/index.php/constellations/article/download/16286/13074

This is an excellent paper on the topic if you want to read more.