John Gill Commentary Numbers 31:9

"And the children of Israel took captive the women of Midian and their little ones; and all their cattle, and all their flocks, and all their goods, they took for a prey." — Numbers 31:9 (ASV)

And the children of Israel took [all] the women of Midian
captives
The word "all" is not in the original text, nor should it be supplied; for if all had been taken, and carried captive, and put to death, as those were afterwards, how could there have been such an increase of the Midianites as there was in some time after this? see (Judges 6:1–6) but the meaning is, that as many as fell into their hands they took and carried captive:

and their little ones ;
both male and female:

and took the spoil of all their cattle, and all their flocks ;
their oxen and their sheep, and also their asses, as appears by the following account:

and all their goods :
in their houses, their wealth and substance, gold, silver