The Mishna on Amud Beis states:

אָסוּר בַּאֲכִילָה וּבִשְׁתִיָּה וּבִרְחִיצָה וּבְסִיכָה וּבִנְעִילַת הַסַּנְדָּל, וּבְתַשְׁמִישׁ הַמִּטָּה. וְהַמֶּלֶךְ וְהַכַּלָּה יִרְחֲצוּ אֶת פְּנֵיהֶם, וְהַחַיָּה תִּנְעוֹל אֶת הַסַּנְדָּל, דִּבְרֵי רַבִּי אֱלִיעֶזֶר. וַחֲכָמִים אוֹסְרִין.

On Yom Kippur, the day on which there is a mitzva by Torah law to afflict oneself, it is prohibited to engage in eating and in drinking, and in bathing, and in smearing oil on one’s body, and in wearing shoes, and in conjugal relations.

This reminds me of a true, funny and sad story, which underscores the importance of appropriate halakhic sex education for children, and the danger and absurdity of avoiding it:

Since there are dozens of halakhos that are impossible to understand without knowledge of the mechanics of human sexual intercourse and reproduction, in truth, one can justifiably argue that teaching a child about sex is part and parcel of the commandment to teach Torah.  After all, how can one possibly teach the laws of family purity, the laws of sexual immorality and the laws of marriage without also teaching about sexual matters?  

Despite many pages of Gemara containing frank and sexually explicit material and incredible risks of overexposure from non-kosher and dangerous sources, sex education is far from a routine or consistent practice in Jewish homes.  The cause of this seems to be a sense of shame and embarrassment associated with sexual matters which, in part, do have basis in the Jewish ethic of modesty, but also may also have a basis in a mistakenly adopted puritanical attitude toward sexuality.

The Gemara is clear that it is inadvisable to lie to a child, even about halakhic matters of expedience, lest as the child grows older he will learn to lie (Succah 46b.)  Furthermore, Maharshal (Yam Shel Shlomo, Bava Kama, 4, Piska 9) indicates one should even martyr himself before succumbing to pressure to misrepresent a Torah fact.

My father Z”L, a veteran mechanech for over 60 years, was very much against misrepresentation of Gemaras that relate to sexual matters. Here is one vignette from his career that aptly illustrates this point. As our Mishna states, there is a requirement of five abstentions or afflictions (Yoma 73b).  They are:  

(1) Eating and drinking; (2) Washing/bathing; (3) Anointing or smoothing oil on one's skin; (4) Wearing leather shoes; (5) Sexual intercourse.

The astute reader will note that actually it appears as if there are six abstentions: Eating, drinking, washing/bathing, anointing, wearing leather shoes and sexual intercourse.  However, the Gemara counts eating and drinking as part of one category, that is, the intake of food.  

As principal of his school, my father Z”L, was observing one of his teachers teach this lesson and noticed that she described the five abstentions as follows:

(1) Eating; (2) Drinking; (3) Washing/bathing; (4) Anointing or smoothing oil on one's skin; (5) Wearing leather shoes.

What's missing here?  Obviously, the teacher wanted to preserve the concept of "five abstentions" but at the same time, wanted to avoid mentioning sexual intercourse.  So the teacher cleverly expanded "eating and drinking" into two separate categories.  Unfortunately, this is in direct contradiction to the Mishna's clear enumeration of eating and drinking as one abstention!  Even though this distortion is perhaps better than the educationally abhorrent practice of mistranslating "tashmish hamittah" as "making the bed", it still is committing Torah forgery. My father confronted her about this distortion of the Torah, but the teacher was resolute in her stance that it would be inappropriate to teach children about sex.  My father explained, "I am not requiring you to teach all five abstentions.  Rather, tell them there are five abstentions but we will study four of them.  Just please do not mislabel them from their original Mishnaic definitions!"  At the time of that story, my father was was young and idealistic, and the teacher was a veteran and set in her ways.  The whole matter turned into an unpleasant confrontation and power struggle.

This story would be a good enough illustration -- but there is a tragic and comic postscript to this story.  Twenty years later, once again my father happened to be observing a class and once again saw a young teacher teaching the "censored version" of the five afflictions.  Now being wiser, less of a kanai and more empathic, my father diplomatically attempted to correct the young teacher. He said, “Aha...you are trying to teach the children about the five abstentions without mentioning sexual intercourse, so you cleverly turned eating and drinking into two separate categories and eschewed sex.  That is an interesting approach, but aren't you concerned that they may never learn it correctly?"  To which the young teacher responded, "Sex?  What do you mean?  Aren't these the five abstentions?"  Clearly, the young lady had no idea that sexual intercourse was one of the five abstentions.  In his own lengthy career my father witnessed both the distortion, and the pathetic product of that very distortion -- a mature woman, a teacher of Torah no less, who was ignorant of a basic Jewish law!  

Ignorance of Torah is not the only casualty of a poor sex education. Children will be exposed to sexuality one way or another, and without adequate preparation and guidance as to the proper Torah perspective, they are more likely to fall victim to abuse, manipulation, or just plain immorality. Even in previous generations I am unconvinced that true Torah homes with a proper mesorah ever held back from teaching children about sexuality out of modesty. But if someone will claim that it was so, surely such with holding today would fit into the category of chasid shoteh, a pious fool (Sotah 21b.)