Kid at JFK
It could seem harmless that a kid issues a take-off clearance or tells a pilot to switch to departure frequency BUT this has to do with licenses and training and even more with confidence in ATC from the pilot side.
It's true that there are trainees who are working the frequencies but they have been through intensive training in ATC academies before being allowed into position together with an instructor.
So, boring as it may be, this is far from OK. Anyone who lets an untrained person work the frequency is not the responsible person who should be in this type of profession.