In Calvin's commentary on Psalm 127:3, he once again asserts God's sovereignty in every area of life. (Emphases mine.)
Lo! children are the heritage of Jehovah. Solomon here adduces one instance in which, in a particular manner, he would have us to recognize the truth which he has hitherto asserted generally -- that the life of men is governed by God. Nothing seems more natural than for men to be produced of men. The majority of mankind dream, that after God had once ordained this at the beginning, children were thenceforth begotten solely by a secret instinct of nature, God ceasing to interfere in the matter; and even those who are endued with some sense of piety, although they may not deny that He is the Father and Creator of the human race, yet do not acknowledge that his providential care descends to this particular case, but rather think that men are created by a certain universal motion. With the view of correcting this preposterous error, Solomon calls children the heritage of God, and the fruit of the womb his gift; for the Hebrew word skr, sachar, translated reward, signifies whatever benefits God bestows upon men, as is plainly manifest from many passages of Scripture. The meaning then is, that, children are not the fruit of chance, but that God, as it seems good to him, distributes to every man his share of them. Moreover, as the Prophet repeats the same thing twice, heritage and reward are to be understood as equivalent; for both these terms are set in opposition to fortune, or the strength of men. The stronger a man is he seems so much the better fitted for procreation. Solomon declares on the contrary, that those become fathers to whom God vouchsafes that honor.