Did you buy the headphones specifically for this or will he get other use out of them?
Just asking because I would expect that they will provide some sort of head phone and it will be something the pilot can communicate to those on the tour. We have done a helicopter tour and an airplane tour on different trips to Hawaii and in prep for our upcoming Alaska cruise my friend shared his pics from a glacier flight and every one of them had similar headphones. Our son, who is not fond of loud noise, did fine on the volcano tour flight.
If you don’t really need them maybe you can return them or more importantly prep your son that they may have “special” headphones that the pilot can talk to you.