Risen from the Dust
One of the most commonly held beliefs about the millennium is that there will be flesh children born during this period. However, this is clearly inconsistent with the idea of a purely spiritual millennium, in which the intangible things replace the tangible things of the world.
Jesus himself speaks directly to this issue, when he is asked a question about marriage in the resurrection, "There were therefore seven brethren: and the first took a wife, and died without children. And the second took her to wife, and he died childless...Therefore in the resurrection whose wife of them is she?...And Jesus answering said unto them, The children of this world [eon] marry, and are given in marriage: But they which shall be accounted worthy to obtain that world [eon], and the resurrection from the dead, neither marry, nor are given in marriage: Neither can they die any more: for they are equal unto the angels; and are the children of God, being the children of the resurrection" (Luke 20.29-36 KJV bible).
Here Jesus makes several things clear about marriage in the millennium. We know that the children of this age (or eon) partake in marriage, because it is the age of flesh man. However, he tells us that the ones who are counted worthy to partake in the resurrection of the righteous, will not be giving or taking in marriage. Now, if we know for a fact that the first resurrection occurs before the millennium, (see ch.19 Seventh Trumpet), then there cannot be any marriage in the millennium.
The saints will not be giving and taking in marriage after the resurrection, because they will become like the angels, having everlasting spiritual bodies. These spiritual bodies are not made male and female, but rather exist on a higher level, without a desire or purpose for marriage. We can also rule out the rest of humanity as giving and taking in marriage during the millennium, because they will be spiritually captive to Hades, or the dust of the earth. They will not have any kind of body to speak of, either flesh or spiritual, and will therefore not be able to rear children. Lastly, there will be no need for children to be born in the millennium, because all people from all generations will already be in the world (see ch.24 Millennium People).
If we assume that this reasoning is correct, and that there will be no children in the millennium, then we have an apparent contradiction. There are a number of Old Testament passages that clearly describe children in the world during the millennium. For example Isaiah 11 says, "The nursing child will play by the hole of the cobra, And the weaned child will put his hand on the viper's den. They will not hurt or destroy in all My holy mountain, For the earth will be full of the knowledge of the LORD. As the waters cover the sea" (Isaiah 11.8-9 NASB bible). How can this prophecy be fulfilled if there will not be any flesh people during the millennium?
To understand the deeper meaning of this, and similar millennium passages, we must first reevaluate the nature of children in scripture. In the bible, there are of course children that are offspring according to the flesh, but there is also another kind of offspring; children after the spirit. For example, we know that Paul was never married or had children (1st Corinthians 7.9), yet in his letter to the Corinthians, he describes himself as their father in Christ, "For though ye have ten thousand instructors in Christ, yet have ye not many fathers: for in Christ Jesus I have begotten you through the gospel" (1st Corinthians 4.15 KJV bible) (see also 2nd Timothy 1.2). Paul addresses them as his children in Christ because he fathered them, not according to the flesh, but according to the spirit.
In fact, all Christians are the spiritual descendants of Christ, born again, not according to flesh, but according to the spirit (John 3.5). That Christ would father spiritual offspring is prophesied in Isaiah, "Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the LORD shall prosper in his hand" (Isaiah 53.10 KJV bible). Christians are the spiritual descendents of Christ, and as they bring new people into the fold those ones become their sons and daughters, and brothers and sisters in the gospel.
All true Christians are related to one another in spirit, being brethren of the same family. This is why Jesus says, "And it was told him by certain which said, Thy mother and thy brethren stand without, desiring to see thee. And he answered and said unto them, My mother and my brethren are these which hear the word of God, and do it" (Luke 8.20-21 KJV bible). Only those who hear the Word of God, and do it, are part of the spiritual family of Christ. Jesus says, "Verily I say unto you, There is no man that hath left house, or brethren, or sisters, or father, or mother, or wife, or children, or lands, for my sake, and the gospel's, But he shall receive an hundredfold now in this time, houses, and brethren, and sisters, and mothers, and children, and lands, with persecutions" (Mark 10.29-30 KJV bible). Those who give up natural families for the sake of the gospel will receive much more at this time (in terms of their extended spiritual families), along with persecutions.
We already know that the millennium will be a time of teaching and wisdom, when the multitudes will go up to Jerusalem to learn the ways and knowledge of the Lord (see ch.26 Millennium Nations). As these ones go up and seek the Lord, they will become as little children in the spiritual sense, because they will grow and mature in him. Therefore, the so-called millennial children are actually references to these converts from the nations (nonbelievers), who will become spiritual progeny as they are nurtured in God's wisdom and love.
Thus, we can better understand the nature of the millennium children written of in Isaiah 65, "There shall be no more thence an infant of days, nor an old man that hath not filled his days: for the child shall die an hundred years old; but the sinner being an hundred years old shall be accursed" (Isaiah 65.20 KJV bible). There will no longer be an infant or old man who dies prematurely, because there will no longer be any flesh. However, the spiritual child will die at an age of one hundred in the sense that he or she will pass into adulthood. In contrast, the sinner who hasn't learned anything after a hundred years, and still abides in their old ways, will be thought accursed. So there is a process of spiritual maturation that will take place in the millennium, as the multitudes are initiated into the ways and knowledge of the Lord.
These spiritual children of the millennium will not be birthed by the flesh, but rather converted in spirit. This is why they are described as being carried to Jerusalem by the nations, "Behold, I will lift up mine hand to the Gentiles, and set up my standard to the people: and they shall bring thy sons in their arms, and thy daughters shall be carried upon their shoulders" (Isaiah 49.22 KJV bible), "Surely the isles shall wait for me, and the ships of Tarshish first, to bring thy sons from far, their silver and their gold with them, unto the name of the LORD thy God" (Isaiah 60.9 KJV bible). However, in Isaiah 66, instead of being described as sons and daughters, these same converts are described as brothers and sisters, "And they shall bring all your brethren for an offering unto the LORD out of all nations upon horses, and in chariots, and in litters, and upon mules, and upon swift beasts, to my holy mountain Jerusalem" (Isaiah 66.20 KJV bible).
What these passages have in common, is that they describe the millennium converts becoming part of the family of God's children. They will be spiritually taken into the fold of his nation. This is why concerning God's elect in the millennium it says, "A little one shall become a thousand, and a small one a strong nation: I the LORD will hasten it in his time" (Isaiah 60.22 KJV bible), (see also Isaiah 61.9). As God's servants teach and lead the nations, they will gather in and multiply spiritual children to themselves, becoming the leaders of large families.
However, keep in mind that these millennium children will remain in their sins, and be held captive to the dust of the earth throughout the thousand year period. They will be taught and led, because there will be no stumbling blocks or satanic strongholds in the world (see ch.26 Millennium Nations). However, they will have to wait until Judgment Day, for Christ to both forgive their sins and personally reconcile them to himself, as Sons of God (see ch.18 Second Resurrection).