613 Mitzvot
Negative Mitzvot 7
Not to pass your children through the fire to Molech

Vayikra (Leviticus) 18:21
Umizar'acha lo-titen leha'avir lamolech velo techalel et-shem Eloheycha ani YHVH.
And your offspring you shall not deliver over to pass through to Molech, and do not profane the name (chillul hashem) of your Elohim: I am YHVH.

Molech is a god of the Ammonites and the Phoenicians. He is also called Moloch. The worship of Molech required that children be used for the ritual ceremony. There is also a New Covenant reference that provides a clue to the identity of this idol:

Ac 7:43  You took up the tent of Molekh, the star of your god Reifan, the figures which you made to worship. I will carry you away beyond Bavel.

Another reference to this practice is Devarim (Deuteronomy) 18:10:
There shall not be found with you anyone who makes his son or his daughter to pass through the fire, one who uses divination, one who practices sorcery, or an enchanter, or a sorcerer,

Although this passage does not specifically mention Molech, the language is the same. It does give us more information about the practice. Molech He was seen as the consuming and destroying and also at the same time the purifying fire.

2 Melakhim (Kings) 17:17  They caused their sons and their daughters to pass through the fire, and used divination and enchantments, and sold themselves to do that which was evil in the sight of YHVH, to provoke him to anger.

Both of these passages use the Hebrew word rbe ('abar). It means to cross over. It is the root for the word Hebrew. Some say that the initiation rite consisted of crossing a platform between two large fires, while others say that it consisted of jumping over a fire (Sanhedrin 64b; Rashi; Radak, Sherashim; Yad, Avodath Kokhavim 6:3; cf. Kesef Mishneh ad loc.)

Talmud Sanhedrin 7 details this practice and tells us that a fire was kindled, and the father handed some of his children over to an idolatrous priest who then caused the children to pass through the fire from one side to another. Rambam also explains that the child was not burned in this ritual (Mishnah Torah, Mada, Hilchoth, Abodah Kochabim VI, 3).

Usually, the practice did not involve human sacrifice, although sometimes it did.

Yirmeyahu (Jeremiah) 7:31  They have built the high places of Tofet, which is in the valley of the son of Hinnom, to burn their sons and their daughters in the fire; which I didn't command, nor did it come into my mind.

Yirmeyahu (Jeremiah) 19:5  and have built the high places of Ba'al, to burn their sons in the fire for burnt offerings to Ba'al; which I didn't command, nor spoke it, neither came it into my mind:

Yechezkel (Ezekiel) 23:37  For they have committed adultery, and blood is in their hands; and with their idols have they committed adultery; and they have also caused their sons, whom they bore to me, to pass through to them to be devoured.

Ibn Ezra said that the practice was a trial by fire, in which the child could be killed.

The context of this mitzvot is among prohibits of all types of sexual perversions. So it is possible that it might have involved some sexual aspects to it. The other reference (Devarim/Deuteronomy) 18:10 has its context in prohibitions against occulting practices. The rite associated with Molech worship may have been a combination of acceptance of the occultic principles of the god-king and initiation of a male child into manhood by allowing access to the ritual prostitutes. This may have all taken place after the child walked through some sort of 'wall of fire' as a symbol of purification. Whatever the act involved, it appeared to be both occultic and sexual in nature.

Tehillim (Psalms) 106:37  Yes, they sacrificed their sons and their daughters to demons.

This is the real heart of the mitzvot.

Today, the practice doesn't seem that common except in some occultic religions. However there are things in this society that a parent can allow their children to be exposed to. There is a lot things that seem innocent, but actually have occultic roots.  I think of things like Pokemon and Harry Potter. Many of the so-called children's cartoons and on TV and video games  have occultic elements in them. Today's children are exposed to all kinds of occultic, violent and sexual things through the media and video games. This in my mind, is the same thing as given them over to Molech.