I am equally amazed that anyone at all escaped this accident with their life, as the little boy(?) did. I cannot grasp how he survived the sheer destruction of this magnitude. Would be interesting to note, for me anyway, where the 10 year old was sitting at the time. Not that it really matters but did his location have something to do with his survival? Or was it just a matter of plain ol' good luck?
The survival aspects will be addressed in the accident report. Given this was a long duration, overnight flight with a 40% passenger load, even knowing the assigned seating for the boy is likely meaningless due to possible reseating after takeoff. Only the survivor knows for sure where he was sitting and I'm not sure I'd expect a 10 year old to recall a seat number.
All that being said, in this accident the largest section of the cabin that remained was the tail. Once separated from the balance of the aircraft, this section had would have offered a high-drag, low-lift profile with no thrust from the engines to offset it. Contact with the ground would occur rapidly, if it were not already in contact at the point of breakup. The final resting position of the tail requires it to have rotated at least 180 degrees, during which aerodynamic drag would have further increased. Until we know where along the airframe the tail separated, it isn't possible to say how much of the forward end of the tail section was consumed by contact with the ground. However, all these factors, plus the lack of post-crash fire in this area, suggest that the tail provided best combination of protection and deceleration in this accident.
The smaller size of a child also reduces the moment arm as the upper body rotates forward and downward around the seatbelted waist, as well as reducing the potential impact of the head against the seat in front. The same factors might be of some value in the tumbling that may have also taken place. These factors are somewhat offset by the weaker bone structure, especially with respect to the skull. As I recall that the child suffered multiple leg fractures which required surgery.