וְאָמַ֞ר הַדּ֣וֹר הָֽאַחֲר֗וֹן בְּנֵיכֶם֙ אֲשֶׁ֤ר יָק֙וּמוּ֙ מֵאַ֣חֲרֵיכֶ֔ם וְהַ֨נָּכְרִ֔י אֲשֶׁ֥ר יָבֹ֖א מֵאֶ֣רֶץ רְחוֹקָ֑ה וְ֠רָאוּ אֶת־מַכּ֞וֹת הָאָ֤רֶץ הַהִוא֙ וְאֶת־תַּ֣חֲלֻאֶ֔יהָ אֲשֶׁר־חִלָּ֥ה יְהוָ֖ה בָּֽהּ׃
און דער שפּעטערדיקער דָור, אײַערע קינדער װאָס װעלן אױפֿשטײן נאָך אײַך, און דער פֿרעמדער װאָס װעט קומען פֿון אַ װײַטן לאַנד, װעלן זאָגן: – װען זײ װעלן זען די פּלאָגן פֿון דעם דאָזיקן לאַנד, און אירע קרענק מיט װאָס גאָט האָט עס קראַנק געמאַכט;
Chizkuni
ואמר הדור הארון, “and the next generation will say, etc.” Moses refers to a generation that had not yet been born at the time when this covenant was entered into by the Jewish people.
Ramban
AND THE REMOTE GENERATION, YOUR CHILDREN THAT SHALL RISE UP AFTER YOU, SHALL SAY. For the tribes of Israel in the first generation already knew [the cause of the disaster] for they heard the imprecations of the covenant [and therefore he states that the future generation will inquire into the cause of the disaster]. It is possible that this verse refers back to the root that beareth gall and wormwood,33Succah 52b. that when this occurs in future generations, they will inquire into its cause.
Ibn Ezra
The future generation denotes both your children and the foreigners who will observe the plagues of the land.