In The Giver families that want to have children must go through an application process. Rules are everywhere in the book, and the governing body controls everything. It even controls family structure. Adults are matched up by a committee of elders, and the adults are paired together based on supposed compatible characteristics.
The couples are not permitted to have their own biological children. Specific women from the community are chosen to be birth mothers. After a child is born, it is then raised by a group of caregivers called "Nurturers." The Nurturers collectively raise children until a child is one year old. At that point the child is assigned to a couple that has been married for a minimum of three years and has completed the application process. Additionally, each family is only allowed to apply for two children. One will be a male, and the other will be a female.
Two children – one male, one female – to each family unit. It was written very clearly in the rules.