While many trekking routes never venture into altitudes high enough to be a potential danger, others do. Big mountains need to be treated with the same sort of respect that big bodies of water or extreme sports require. Despite every precaution and effort we take, trekking at altitudes above 3000 m. / 10,000 feet is not a risk-free experience.
The primary precaution on high routes is to ascend at a pace proven by years of experience to allow most people to acclimatize safely. Our itinerary plans always take this into account. Your participation in safety is also key. Your guide will ask constantly how you feel. You must be direct and honest. Acclimatization difficulties are easily remedied in their early stages. The simplest and almost always effective action is to stop ascending and, if necessary, descend. Even a few hundred meters can make a big difference. We expect you to be an active participant in your safety. The only people who get into serious problems with altitude are the Type A folks who focus on their goal rather than on safety.
For this reason we do not take pre-teen children above 3000 m. / 10,000 feet without extensive conversation with their parents or guardians. Young children usually do not have the ability to self-assess and report on their condition. There are exceptions, but we strongly recommend that families with smaller children stick to one of the many beautiful lower-altitude routes.
And we want all trekkers to take out travel insurance, even if you don't normally do so when you travel. Coverage for trip interruption and lost baggage can come in very useful, but the important coverage to have is for medical evacuation and repatriation. Helicopter evacuation from a remote area can cost thousands of dollars. Low risk, expensive eventualities are exactly what insurance is for.