Jer 2:30 “In vain [shawv] I have chastened [naw-kaw’] your children; They received no correction. Your sword has devoured your prophets like a destroying lion.

In Jeremiah 2, God is lamenting that Israel has abandoned Him. In this chapter, God details His blessings for Israel and His reproofs of Israel. God cannot understand why Israel is so stubborn, to reject Him in favor of false gods. In Jeremiah 2:30, God declares that He has killed [naw-kaw’] their children. Children might be a general term for Israel, such as “Children of Israel”, but there is a strong theme in Jeremiah of punishing families including children. God uses the death of children as the ultimate punishment against the wicked. After all, what else can break a man besides the death of his children? The word naw-kaw’ can mean “punish”, but it is often used for slaying within Jeremiah and within the Bible. The interesting thing is that the verse says this slaughter or punishment was done “in vain”. The most heartbreaking act imaginable did not stir the hearts of Israel.

This word literally means “without profit”:

Mal 3:14 You have said, ‘It is useless [shawv] to serve God; What profit is it that we have kept His ordinance, And that we have walked as mourners Before the LORD of hosts?

So God is punishing Israel and the punishment is done without the desired results (or any results). God’s punishment did not accomplish what He wanted. It was a wasted act. This does not sit well with those who believe God knows the future in detail. If that is the case, God is killing people for no reason at all. The text is meant by the author to communicate that God expected His punishment to result in repentance. God’s reason for punishment was the possibility of repentance.

Throughout Jeremiah, God details His ongoing plans to punish Israel, including punishing the families and children of the wicked:

Jer 6:11 Therefore I am full of the fury of the LORD. I am weary of holding it in. “I will pour it out on the children outside, And on the assembly of young men together; For even the husband shall be taken with the wife, The aged with him who is full of days.

Jer 9:21 For death has come through our windows, Has entered our palaces, To kill off the children—no longer to be outside! And the young men—no longer on the streets! [God says He will cause this in Jer 9:15]

Jer 11:22 therefore thus says the LORD of hosts: ‘Behold, I will punish them. The young men shall die by the sword, their sons and their daughters shall die by famine;

Jer 15:7 And I will winnow them with a winnowing fan in the gates of the land; I will bereave them of children; I will destroy My people, Since they do not return from their ways.

Jer 16:3 For thus says the LORD concerning the sons and daughters who are born in this place, and concerning their mothers who bore them and their fathers who begot them in this land:
Jer 16:4 “They shall die gruesome deaths; they shall not be lamented nor shall they be buried, but they shall be like refuse on the face of the earth. They shall be consumed by the sword and by famine, and their corpses shall be meat for the birds of heaven and for the beasts of the earth.” [God says He will do this in Jer 16:9]
Jer 18:21 Therefore deliver up their children to the famine, And pour out their blood By the force of the sword; Let their wives become widows And bereaved of their children. Let their men be put to death, Their young men be slain By the sword in battle. [This is Jeremiah asking God to do this]

Jer 29:32 therefore thus says the LORD: Behold, I will punish Shemaiah the Nehelamite and his family: he shall not have anyone to dwell among this people, nor shall he see the good that I will do for My people, says the LORD, because he has taught rebellion against the LORD.

In Jeremiah, the people as a whole have rebelled. The punishment then falls on not only them, but their children. But God will not always operate like this. Jeremiah states that at some point in the future, God will begin only punishing those who deserve to be punished and not their children.

In other words, God will be changing His operating procedures. In Jeremiah 31, God begins describing Israel after they have returned to Him and after God has shown mercy to them. It is at this time God will begin punishing each person for their own sins:

Jer 31:27 “Behold, the days are coming, says the LORD, that I will sow the house of Israel and the house of Judah with the seed of man and the seed of beast.
Jer 31:28 And it shall come to pass, that as I have watched over them to pluck up, to break down, to throw down, to destroy, and to afflict, so I will watch over them to build and to plant, says the LORD.
Jer 31:29 In those days they shall say no more: ‘The fathers have eaten sour grapes, And the children’s teeth are set on edge.’
Jer 31:30 But every one shall die for his own iniquity; every man who eats the sour grapes, his teeth shall be set on edge.

The Hebrew idiom at the time was that ‘The fathers have eaten sour grapes, And the children’s teeth are set on edge.’ Jeremiah explains the reversal of the idiom, which is useful if the idiom is not obvious to modern readers. The illustration is that the father is eating something bad and the children taste it. This idiom meant that when the father sinned, then God punished even the children.

Jeremiah means for this saying to be dissolved in Israel (not right away, but at some future point). At that time, God will reverse that saying. People will begin to die for their own sins, not the sins of their fathers. In Ezekiel’s time, God seems to have embraced this fully in reference to Israel:

Eze 18:2 “What do you mean when you use this proverb concerning the land of Israel, saying: ‘The fathers have eaten sour grapes, And the children’s teeth are set on edge’?
Eze 18:3 “As I live,” says the Lord GOD, “you shall no longer use this proverb in Israel.
Eze 18:4 “Behold, all souls are Mine; The soul of the father As well as the soul of the son is Mine; The soul who sins shall die.

When God revoked this proverb, it was in relation to Israel’s use. Jeremiah had confirmed the general applicability during his own time. Ezekiel does away with it. The proverb still applies to foreign peoples who are generally wicked. The general principle in all of this seems to be that if a nation is exceedingly wicked, God is justified in complete destruction. If the people are passive, then God judges each according to their works.