There wouldn't have been that many kids, or rather there would have been plenty of adults.
The bathing station was a phenomenon of the 1930s and lasted until the war. Born of the fitness and health movement, which was largely an adult thing, with events geared around adult events and exercise, games, diving, and exhibitions by swimming 'stars' of the time. Many games and events were held in the water too, and there were even 'Midnight swims' under floodlight - but I do not know if this was a feature at Rothesay. There is not enough history to hand. All but a handful of these outdoor pools remain in operation today. For example Gourock and Stonehaven.