While the indication from earlier verses does confirm the practice of child sacrifice (see Isa. 57:5), these texts are comparisons to make a point.
God did not delight in animal sacrifice (Psa. 51:16; 1 Sam. 15:22; Hos. 6:6).
"11 To what purpose is the multitude of your sacrifices unto me? saith the Lord: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats.
12 When ye come to appear before me, who hath required this at your hand, to tread my courts?
13 Bring no more vain oblations; incense is an abomination unto me; the new moons and sabbaths, the calling of assemblies, I cannot away with; it is iniquity, even the solemn meeting." (Isa. 1:11-13, KJV)
The institution of animal sacrifices - sin offerings - was to impress upon the mind of man that sin results in death (Rom. 6:23). Each time they had to place their hand upon the head of the lamb they brought, or the bull/ox, or the goat, they were transferring their sin to that of the animal (Lev. 4:4, 15, 24, 29). Thus, the animals became "sin" in God's eyes.
Thus, "to make an end of sins" in Dan. 9:24 meant making an end of sin offerings. See Adam Clarke's commentary here.
They were to realize that their death sentence was being transferred to an innocent animal, and learn to be repelled by sin. Instead, the people ritualized the sin-offerings and became hard of heart, looking upon the killing of the innocent animal as a "get out of jail free card".
They would commit sins with premeditation, and then go to the priest with a sin offering. The poor animals were being slaughtered before God without any true contrite sorrow, or repentance of the sins committed by the people.
"And if the whole congregation of Israel sin through ignorance,..." (Lev. 4:13, KJV)
"...When a ruler hath sinned, and done somewhat through ignorance against any of the commandments of the Lord ..." (Lev. 4:22, KJV)
"And if any one of the common people sin through ignorance, ..." (Lev. 4:27, KJV)
The comparisons in Isa. 66:3 told the people that they were using God's mercy and forgiveness in order to commit sins, when they should have come with a sorrowful heart for having unintentionally committed a sin. When they brought a bull to be sacrificed, the transference of their sin to the bull meant the bull was dying in their place. God was bringing to their remembrance the gravity of the sin offering by comparing it to a heinous act; that they were the true guilty party, and it was no small thing to sacrifice that animal.
"3 But in those sacrifices there is a remembrance again made of sins every year.
4 For it is not possible that the blood of bulls and of goats should take away sins.
5 Wherefore when he cometh into the world, he saith, Sacrifice and offering thou wouldest not, but a body hast thou prepared me:
6 In burnt offerings and sacrifices for sin thou hast had no pleasure." (KJV)
The types of sacrifices were also compared to the abhorred pagan sacrifices.
Excerpt from Benson's Commentary on Isa. 66:3 -
"The sacrifice of the wicked is an abomination to the Lord. He that sacrificeth a lamb as if he cut off a dog’s neck — Namely, in order to sacrifice it. This animal was held in the greatest abhorrence by the Jews, insomuch that the very price of a dog was forbidden to be brought into the house of the Lord, Deuteronomy 23:18. The comparison shows God’s detestation of ceremonial performances from persons destitute of true piety. He that offereth, &c., as if he offered swine’s blood — Which, being one of the principal sacrifices which the heathen offered to their idols, was in a particular manner abominable to God. He that burneth incense as if he blessed an idol — As if he honoured an idol with gifts and presents. From hence it is plain that the prophet is not here reflecting upon idolatrous worship, but formal worship; for to say, He that burneth incense to an idol is as he that blesseth an idol, would be only to say, He that blesseth an idol, blesseth an idol; that is, it would be saying nothing. But he is reflecting upon those who, in a formal way, and not in spirit and in truth, worshipped the true God, and by acts which he had appointed. God, by the prophet, declares that these men’s services were no more acceptable to him than murder, idolatry, or the most horrid profanation of his name. Yea, they have chosen their own ways — They live as they list; they persist in their wicked practices, and yet expect to recommend themselves to my favour by their ceremonial observances. And their soul delighteth in their abominations — Taking pleasure in their sins, and showing their contempt of my authority and enmity to my holiness, as much as their fathers did when they were mad upon their idols." Source: Biblehub
God wanted their contrite repentant heart, not the death of the animal, or even their deaths. But, they had turned the method of forgiveness into a ritual resembling pagan idolatry.