I am not a doctor, but I watch them on TV ;-) Regardless of when the doctors say the child can physically handle high altitude, I would suggest that a child who can't articulate the signs of AMS is too young. Reading the spectacular trail reports from July when the monsoon and flash flood hit, I was shocked to hear about someone summitting in the hail with a 1-year old baby in a backpack. Even if the average 1 year old can physiologically handle altitude, you would never know if an individual infant can or can't handle the altitude except to try to interpret crankiness or tiredness (normal symptoms for a 1 year old) which may or may not also be their way of manifesting AMS symptoms.
In my non-professional opinion (but as a father of 4 and as one who is cursed with AMS), no child should go up at AMS susceptible altitudes unless they are reliably capable of articulating symptoms or maybe if they have been acclimatized on the most conservative of schedules that all risk and doubt have been removed.
Brent N
