Oxygen on the 767 is supplied by a portable oxygen unit which will be stowed under the seat in front of your son. It is a large gray box that contains a large oxygen bottle. It will be brought by the crew and come with either a non re-breathing oxygen mask or a nasal delivery.

So, effectively, on the 767, any seat apart from emergency exit and bulk head seats can be allocated as there needs to be a seat in front to stow the oxygen unit under.

My colleague has already told you about the 777 and 747 systems.

Hope you have a good trip, any more questions, feel free to ask.