God told Adam and Eve this as part of His blessing to them.
"And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth..." (Genesis 1:28)
Children are a blessing to the parents, and also are part of the pleasure that God receives from His creation. "Thou art worthy, O Lord, to receive glory and honour and power: for Thou hast created all things, and for Thy pleasure they are and were created." (Revelation 4:11)
After the flood, God knew that the survivors may have been reluctant to have large families, after having seen the mass destruction of so many people, so He encouraged them repeatedly in Genesis 8 and 9 to have the confidence to again replenish the earth.
It was in this context that God's 1st covenant with man was given to Noah, (promising that the earth would not be destroyed) as a further reassurance that they should "Be fruitful, and multiply, and replenish the earth". Genesis 9:1 [the first covenant was given in Genesis 9:9-17]
The context of the second covenant, given to Abraham (or Abram), also shows God's mind as to children in the light of being a blessing. "Look now toward heaven, and tell the stars, if thou be able to number them: and He said unto him, So shall thy seed be." (Genesis 15:5) [the 2nd covenant was given in verse 18]
God stresses this point to the Children of Israel, telling them that having children was part of His blessing to them. See, for instance Deuteronomy 7:13 "Thou shalt be blessed above all people: there shall not be male or female barren among you."
In the New Testament we find that the act of raising children was considered a merit. For instance widows were to be cared for if she were "well reported of for good works; if she have brought up children..." (1 Timothy 5:10), and the younger women (in verse fourteen) "that the younger women marry, bear children, guide the house..."
As for the men, children were also listed in the description of what traits were to be seen in an "elder" and a "deacon" in 1 Timothy 3.
Certainly an added blessing for Christians is to see their children "grow in grace, and in the knowledge of our Lord and Savior". As John wrote to "the elect lady, and her children" in his second epistle, "I rejoiced greatly that I found of thy children walking in truth, as we have received a commandment from the Father." (See verses 1 & 4)
"Lo, children are an heritage of the Lord: and the fruit of the womb is His reward." (Psalm 127:3)