How is it possible that their garments did not wear out during their entire stay in the desert?
Rashi and Ramban (citing the Midrash): Because the Ananei Kavod washed and ironed them even whilst they wore them. Moreover, they also caused the children's' clothes to grow together with them. 1
Why did their feet not swell in the way of people who walk barefoot in the desert?
Targum Onkelos: The Torah means that their shoes did not wear out (presumably for the same reason as their clothes. 1
Targum Yonasan: Because their shoes, like their clothes, remained intact throughout the forty years that they traveled in the desert. 2