The claim is nicknames are created because there are children.
Children name themselves or their brothers and sisters by choosing a word they can say.
This ignores the capriciousness of the parental element. The moment of leaning over the crib, basket, or blanket. The parent's mouth shaping the nameword. If you are a child you will be called Mama, Poupette, Peanut, Junior, Niecey, or Littleman. These are nonnegotiable.