Thanks for the responses suggestions and good wishes.
I have emailed the airline and an waiting on a response.
Just for clarity. The ear defenders are not electronic so no issues from that perspective. Ideally he will wear them when boarding (they are as much a comforter as anything else), so no chance of hiding them (and their being day glo yellow!).
I have been a very frequent flyer for more than 20 years (perhaps a thousand flights, really lost count). So I have enough respect for the CC to not argue, deceive, or generally try to pee them off. So if it's "no" on the day then it's no and i will just have to deal with it.