Your son is correct that the winged prop was used as AAC/AAF cadet cap insignia,BUT it was also widely used by the AAF,not just aviation cadets. You will see it as collar insignia on both officers and enlisted uniforms for example.

These belt buckles are more likely private purchase as offered through PX’s and military outfitters and would have been bought by AAF officers(and possibly enlisted men too). They would not be issued to air cadets as a part of their uniform.

Garry.