Adam Clarke on Numbers 32:16

We will build - cities for our little ones - It was impossible for these, numerous as they might be, to build cities and fortify them for the defense of their families in their absence. Calmet supposes they meant no more than repairing the cities of the Amorites which they had lately taken; which work might have been very easily accomplished in the time which they spent on this side of Jordan, before they went over with their brethren, to put them in possession of the land.