BFSGrad. I find it highly likely that a two-year-old would fall soundly asleep amidst the gentle hum and vibration of a relatively short airplane trip.
However, I’ve joked with others about the “baby barometer,” perhaps more applicable to infants, who have trouble clearing their ears and start wailing when the plane begins to descend.
I assume that one or both of the adults in the passenger cabin might have been checking their watches and the ETA as they were trying to go elsewhere upon arrival.
The lack of ATC communication happened extremely early into this trip, and we don’t know why, but hypoxia would go a long way to explain it. As to the passengers, per the Washington Post article I cited earlier, they’d known this particular pilot a long time and presumably weren’t strangers to the cockpit.
And yes, frost on the windows does reflect an abrupt loss of pressure at high altitude, not a slow leak. After all, when you hike up a mountain, the air gets thinner, but you don’t see your breath crystallize until it is really, really cold.
With a slow pressure leak, I assume the humidity from your breath in the cabin would leak away too, hence less to cause the windows to ice up.
PV = nRT. Pressure drop = temperature drop. Avogadro’s law. Ideal pressure law.
Pure speculation on my part.