Could it be the stewardesses survived because they were in rear facing seats and the kid because of the lower body mass?
Early reports suggested that the two flight attendants had survived, but they turned out not to be true. The three survivors were all passengers.
The aircraft was supposedly configured with cargo pallets toward the front, and only 24 seats at the rear. With this arrangement, survivability would be more luck than anything else, and it would only be baseless speculation to suggest why one passenger survived and another didn't with the information available now.