As I continue my research into the nature of Israelite child sacrifice in the Old Testament I am struck by the differences between the “Molech Cult” (e.g. Leviticus 21:1-5; Jeremiah 19) and the mysterious instances in which firstborn heirs were offered (or almost offered) as a sacrifice to Yahweh (Genesis 22; Judges 11).
The Molech sacrifice was carried out in a specific way (whole burnt offering by fire), to a specific deity (either Baal or Molech), in a specific place (Hinnom Valley, Jerusalem), for a specific purpose (divination/fortune telling), and with an unspecified type of offering (a son, a daughter or multiple children).

Carthage topheth, wikimedia commons
The rare instances of Yahwistic child sacrifice – Abraham and Isaac (almost), Jephthah and his daughter and possibly Mesha and his heir (2 Kings 3:27) were carried out in different places (Moriah, Gilead, and Kir-Haresheth), for a different purpose (obedience to and/or seeking salvation from Yahweh), and with a specified type of offering (the firstborn or beloved son of the family).
The best two texts for seeing the differences between the two practices are Jeremiah 32:33-35 and Micah 6:6-8.
“They have turned to me their back and not their face. And though I have taught them persistently, they have not listened to receive instruction. They set up their abominations in the house that is called by my name, to defile it. They built the high places of Baal in the Valley of the Son of Hinnom, to offer up their sons and daughters to Molech, though I did not command them, nor did it enter into my mind, that they should do this abomination, to cause Judah to sin.” (Jeremiah 32:33–35 ESV)
Jeremiah explicitly shows that the Molech cult was against the regulations of Torah. In other places, Jeremiah prophesied that the Hinnom Valley would be so filled with the dead that there would not be any space to bury anyone (e.g. Jeremiah 19). This prophecy would later lead the Hinnom Valley/Cult of Molech to come to be identified with the entrance to hell itself (Talmud) and become the primary name for hell – Gehenna – in the New Testament (Matt. 5:22).
“With what shall I come before the LORD, and bow myself before God on high? Shall I come before him with burnt offerings, with calves a year old? Will the LORD be pleased with thousands of rams, with ten thousands of rivers of oil? Shall I give my firstborn for my transgression, the fruit of my body for the sin of my soul?” He has told you, O man, what is good; and what does the LORD require of you but to do justice, and to love kindness, and to walk humbly with your God?” (Micah 6:6–8 ESV)
“For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.” (John 3:16 NAS95)