Usually the sons mentioned are first-borns. Here is a sample:
When Jared had lived 162 years, he fathered Enoch. Jared lived after he fathered Enoch 800 years and had other sons and daughters…. When Enoch had lived 65 years, he fathered Methuselah. Enoch walked with God after he fathered Methuselah 300 years and had other sons and daughters (Genesis 5:18-19, 21-22).
God attaches significance to first-born males (Genesis 25:24-34; Exodus 13:1-2, 12-15; 22:29; Luke 2:23). The first-born receives special blessings and usually leads in family and religious matters. However, this is not because the first-borns are “better” or “more spiritual.” Many of them prove that they are not (Genesis 38:7; 49:3; Numbers 3:2-4). Their role is simply the position within the family to which God assigns them. God expects them to fill this position, regardless of their personal preferences or comparative abilities. To despise this birthright leads to the gravest consequences, as Esau learns (Genesis 25:34; Hebrews 12:16).