Altitude sickness occurs when someone goes to a high altitude where there is less oxygen than he's used to. Although the concentration of oxygen in the air remains the same (21 percent) at differing altitudes, the number of oxygen molecules per breath goes down as the altitude increases. People have to breathe faster in order to accommodate, and, even so, they won't get as much oxygen as they would at a lower altitude.
Symptoms of altitude sickness include headache, dizziness, shortness of breath, nausea, vomiting, weakness and malaise. An additional side effect is leakage of fluid from the capillaries, which may build up in the lungs or brain and become serious or even life threatening.
Few people have ever been to such high altitudes, so there's not enough data to tell us exactly who will be affected and at what altitudes. The age of the person doesn't seem to be connected to whether or not he or she will experience altitude sickness. Children are as likely to experience it as adults are. Experts recommend that children under the age of two not sleep at an altitude above 6,560 feet (2,000 meters). Some recommend that children aged 10 and under not sleep at an altitude above 9,840 feet (3,000 meters); but others conclude that children old enough to express themselves clearly and vocalize when they are feeling ill should be allowed to sleep at higher altitudes.
Anyone can adapt to pretty much any altitude if they give it enough time. It takes one to three days to acclimatize to any given altitude. If you give your child enough time to adapt he should not get altitude sickness. Altitude sickness arises when going too high to fast or stay up very high for too long. If your child develops altitude sickness and is not able to acclimatize, take him down to a lower altitude immediately.