I think those might be SA Police recruits or perhaps the SAAF band. I will do a bit of digging in my files...
Here are pictures of the light blue with white edging cap bands.
http://saafww2pilots.yolasite.com/zingi-harrison.php
http://saafww2pilots.yolasite.com/arthur-geater.php
My understanding is that they had plain light blue bands at first and blue ones with white edging depending on the phase of training (if anyone can confirm or correct me that would be great!).