First, I would have to say that you need to monitor each incident and respond accordingly. None of my kids (nor any of the other children I have hiked with) has ever had altitude sickness. With adults, however, I have been on 12 trips where someone got sick (nausea and headache). In each case, dropping 1000 to 1500 ft did the job. I have been lucky; over 17000ft and the most I have felt is just winded.