cadet uniform is nearly exactly the same as adult 'black and white' uniform ( cadet badges and different headgear - beret for duties If worn )...
while it's not changing to SDU for cadet activities - because St John Youth didn't want to be part of SDU - 16 - 18 cadets with adult FA competencies should be wearing SDU when it is issued in their locality
As for the operational role of cadets on duty cadet first aiders can treat under supervision and adult role FAs (16 -18s) can treat under the same (minimal) supervision as any inexperienced adult FA, they can also undertake support roles in line with risk assessments and if suitably trained in radio comms and deemed suitable by the CRCO can be control operators or loggists