Notice the quick get-away vehicle, the inability to recognize faces, and the gloves to ensure there are no fingerprints (or armprints).
The outfit they're wearing is the ao dai (pronounced "ow zie," approximately). The shirt has panels that drop to the ankle at front and back. The ao dai is getting commoner and commoner as I head south. In this case I think we're looking at a school uniform but others wear it as well, usually as formal wear. Why the face mask and gloves? As Westerners search for the perfect tan, so Easterners search for the perfect pale (the face mask also helps to filter the air). And the logic here is very much the same as it was in the West during the Victorian age: 'people who work in the fields are dark.' In the West now only those who have leisure time can get a tan. Similarly, women here do everything they can to preserve their pale skin. Nivea even markets skin-whitening cream.
P.S. I'm finding that I sometimes have trouble accessing "gilesorr.com," so the blog may go silent occasionally and even my email may go silent - despite the ever-presence of internet cafes in Vietnam. Connectivity is definitely better to places on this side of the planet, less so to North America.