Continuity mistake: After 70 days in the Andes, Nando has not grown a beard. Two days later, when they come with the choppers, he's managed to grow quite a nice one.
Factual error: While debating when to begin the trek across the Andes with Nando, Roberto remarks that "winter will be over" soon. This incident took place in South America where the seasons are opposite from the northern hemisphere. The plane crashed in the spring and Nando and Roberto reached Chile by foot in the summer.
Factual error: Most of the time the boys have no visible breaths, even though they're in a freezing climate.