I think they should wear the appropriate shoes, whatever the school principle has decided upon. From my point of view, the Lao road traffic authority should make it compulsory for motorbike riders to wear helmets. That will safe lives. There are too many people died from the motorbike accidents.
I think that the sport shoes are not a part of their school uniform, they can wear any kind of shoes that is comfortable on their feet including flip flop shoes.