Originally Posted by
erik123
I think your question is about altitude sickness. If I understand it correctly - infants are not more prone to it - though as they can't communicate the danger signs (dizziness, loss of mental abilities) they are at much higher risk. The only cure is descent - the alternative is death.
As a rule, the unpressurized planes do not climb much higher than the cabins of pressurized planes. And the those altitudes are not really dangerous. Mild mountain sickness may occur, but those altitudes are routinely survived by a lot of adults and children.