Family units are created by a committee. The purpose of the family unit is to raise children between the ages of 1 year and adulthood. There is no love, and families do not have their own children. One male and one female adult are matched based on complementary personalities. Only adults that are deemed to be good potential child-raisers are considered. Other adults remain childless.
Once two adults are paired, they are given one boy and one girl. The pair first apply for a child, one at a time, which is granted by the committee. The family is given a baby once it is named, at the Ceremony of One. Before then, the babies are called by their number only. The babies come from birthmothers, and are likely genetically engineered. The family can only have one boy and one girl at a time. If one of the children dies by accident, the family can apply for another.
It is unusual for the two children to be very far apart in age. Usually there wil not be more than three years difference between the two, but the parents are the ones who decide when to take the second child. There will always be one boy and one girl.
Once the youngest child is grown, the family unit dissolves and there is basically no relationship between the children and adults. The children form family units of their own, and the adults move to the childless adults area.