Or HaChaim on Deuteronomy 31:13/אור החיים על דברים ל״א:י״ג

1 ובניהם אשר לא ידעו, "and their children, who do not know, etc." This division is in line with mention of "and the children" in verse 12 as part of the מצוה of הקהל. Moses says that although he is aware that the children are too young to understand what they would hear at that assembly, they are not too young to learn to fear G'd, i.e. one must train them in יראת השם from an early age.

2This is the reason why Moses changed the sequence in which he described this process. Whereas in verse 12 he had said ילמדו ויראו they would "learn and (as a result) fear," in this verse he says "they will learn to fear." Being present at such an experience as הקהל is inspirational even for young children and inspires fear of G'd. Moses adds the comment כל הימים, "all the days," to remind us that when fear of G'd is instilled in children at an early age it will last them all their lives.

3Our sages (Chagigah 3) ask why the women had to drag their children along for this assembly, and they answer "in order to receive credit for complying with the instruction." Presumably they referred to those children who could not even appreciate that their elders were listening to the Torah, i.e. the babies in arms. They must have understood that Moses' reason for bringing them applied only to children who were already somewhat older.