Oznayim la'Torah: Because, whereas by Hakhel, the women - who understand what is being read, come to listen, and the smll children, only to give reward to those who bring them, here, where Moshe is referring to entering into the B'ris, he gives precedence to the small (male) children, who are destined to grow-up and become Chayav to keep all the Mitzvos, as opposed to he women, who will never be Chayav the Mitzvos Asei that are time-bound.

Oznayim la'Torah #1: Because, whereas in Re'ei, Moshe is referring to after they would settle in Eretz Yisrael, when the Geirim would live among them, here, he is referring to their current encampment in Arvos Mo'av, where they simply sojourned in the midst of the camp.

Oznayim la'Torah: The Torah is hinting that all the Geirim lived in the camp - and were not allowed to settle in Eiver ha'Yarden together with the women and children of Reuven, Gad and half of Menashe, since they could not be trusted not to join any enemy who would come to attach them.

Rashi: This teaches us that Cana'anim came to convert ¹ just as the Giv'onim later came to trick Yehoshua, ² and Moshe appointed them as wood-choppers and water-drawers. ³

Hadar Zekenim and Rosh (both in Pasuk 9) and Da'as Zekenim: They refer to the Avadim and the Shefachos, respectively.

Oznayim la'Torah: He lists the Geirm first because, as opposed to the wood-choppers and water-drawers, who came because they were afraid of Yisrael, they came to convert, ¹ and the wood-chippers before the water-drawers, because, as opposed to the water-drawers, they require a degree of expertise - to ensure that one does ham oneself or someone else in the process.

Refer to 29:10:1:2.