Charles Ellicott Commentary Genesis 21:23

"Now therefore swear unto me here by God that thou wilt not deal falsely with me, nor with my son, nor with my son`s son. But according to the kindness that I have done unto thee, thou shalt do unto me, and to the land wherein thou hast sojourned." — Genesis 21:23 (ASV)

Nor with my son, nor with my son’s son. —The words are not those commonly used for son and grandson, but a Hebrew phrase signifying my kith and kin. They might be translated, “nor with my offshoot nor my offspring.” The words occur again in the same proverbial way in Job 18:19; Isaiah 14:22.