I have two sons, now grown. The younger boy is taller than his brother by several inches. After they had both "matured" the older boy complained that his younger brother had a "bigger one" then he did. I reminded him that his brother had a bigger one than I did, also, which he knew was true, since we had all been naked before each other in our adult years.
It may be a bit of a set-back for any father to know that his sons have bigger cocks than he has, but I would rather have it this way than the other way around. I also told them that I had seen their mother's father and brothers naked and that they had big cocks too, so they got the best from both sides of the family.