I would have taken matters into my own hands and confiscated one of the devices. I then would have had to make sure that indeed it did not cause any inflight problems by "testing" such device until we were near our destination.

If one of the little pax were to try and complain about my appropriation of his device, I would have warned the both of them that the evil FA would take them both away when I ratted that they were using it wireless.