What happens to parents when the kids grow up in The Giver?
When their kids are grown, parents go to live with the Childless Adults, and have little contact with their children after that.
In The Giver, families are carefully planned. Parents are matched based on their child-rearing potential, and assigned children once they apply for them. Parents can apply for one boy and one girl. They can’t have more than two children, and they can’t have more than one of each.
Parents do not conceive their own children, and they do not love them. They are more like caregivers than parents.
Since families only exist for the purpose of raising the children, once the children are grown the family unit disbands. Both adults go to live separately—there relationship was never about the children—and the children eventually will be paired with a spouse and given children of their own, or will live with Childless Adults.
When adults of the community became older, their lives became different. They were no longer needed to create family units. Jonas's own parents, when he and Lily were grown, would go to live with the Childless Adults. (ch 13, p. 102)
The family unit is a practical one. It exists to provide stability and resources. It gives each child more individual attention. The parents care for each other, and care for their children, but they do not love each other or their children and they are not biologically related to them.
The community's solution to child-rearing eliminates some of society's problems. There are no broken homes here. However, it also eliminates one of the main benefits of our messy modern life: LOVE. There is no love, and there is no family of the type we are used to. Both are foreign and intelligible concepts to the people in Jonas's community.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.