TT #7 · Parashas Vayechi · Passuk 48:5
And now thy two sons, who were born unto thee in the land of Mitzrayim before I came unto thee into Mitzrayim, are mine; Efrayim and Menasheh, even as Reuven and Shimon, shall be mine.
Torah Temimah points to Kesubos 72b (and the related discussion of cursing ancestors).
TT lemma: אפרים ומנשה.
English of Core Text: We learned: A woman who curses her husband’s parents in his presence goes out without her kesubah. Rav Yehudah said in the name of Shmuel: Do not say “in his presence” literally, but even if she curses his parents in the presence of his children; and your mnemonic is “Efrayim and Menasheh, even as Reuven and Shimon, shall be mine.”
Asmachta / mnemonic from the verse — the equation of Yosef’s sons with Yaakov’s own sons supports the broader principle that בני בנים הרי הם כבנים.
Grandchildren are regarded as children. Consequently, a wife who curses her husband’s parents in the presence of the grandchildren is liable to lose her kesubah, just as if she had done so in the husband’s own presence.