Under the Old Covenant children were born into the Covenant without any personal choice. Their parents decided to circumcise them on the eight day, and it was up to the parents to teach them and train them in the ways of the Old Covenant. Under the New Covenant, no one in covenant has to be taught to know the Lord because only those who make the decision to follow Christ are in covenant. They are the ones who are born not of flesh but of Spirit. In the age to come/ world above, being married and being given in marriage is not necessary to produce children of God because they are born by the word of truth.
Some additional study helps:
Born of Above: http://labornotinvain.com/2016/10/27/born-of-above/
I am from Above: http://labornotinvain.com/2016/03/16/i-am-from-above/