Things work very differently in the community than in our world. Family units are not quite the same. In the community, a man and a woman are paired by a committee of elders based on perceived compatibility. They are watched carefully for three years, at which time they may apply for a child and are given either one boy or one girl. They can then choose how long they want to wait before they apply for their second child. If they already have a boy, the second child will be a girl, and vice versa. It seems quite common for the boy to come first. After the youngest child grows up and moves out, the family unit is disbanded.
In, The Giver, everything is completely planned out. After a spouse is matched to another and a marriage is arranged, the couple waits three years and is watched by a Committee of Elders. After the three years has passed, if the couple thought to be in good standing and doing well, they may apply for a child.
Pg 48-49 The Giver