Altitude Sickness in Kids at Colorado Ski Resorts

Children get acute mountain sickness (AMS) at roughly the rate adults do. In a study of 558 children aged 9 to 14, published in 1993 in what is now JAMA Pediatrics, 28% met a symptom-based case definition for AMS after ascending from 1,600 m to 2,835 m. That starting elevation is close to Denver's, and the finishing elevation is within a few hundred feet of the Breckenridge and Copper Mountain base villages, which makes the study's ascent profile an unusually close match for a Colorado ski trip.

Sit with the other number from that same study, though. A comparison group of similar-aged children at sea level reported three or more of the same symptoms 21% of the time. Headache, tiredness and a foul mood are not exclusively altitude.

So the realistic expectation for a family flying into Denver and sleeping at 9,000 ft or above that night is this: a decent chance of a headache, poor sleep, an untouched dinner and a grumpy child on day one. A smaller chance of vomiting. A very small chance of anything that requires you to change your plans. Your job is not to prevent the first category. It is to recognize the third.

The CDC's guidance for travelers is that acute acclimatization takes 3 to 5 days, and that acclimatizing for a few days at 8,000 to 9,000 ft before proceeding higher is ideal.

Read that band again. 8,000 to 9,000 ft is not a rest stop on the way to Colorado ski country. It is Colorado ski country. The CDC describes that elevation as the place you pause before going higher. For a family flying into Denver on a Saturday morning, it is where they sleep that night.

That is the whole problem in one sentence. The standard family ski itinerary, sea level at breakfast and mountain town by dinner, compresses an ascent that altitude medicine describes in days into about six hours.

The Medical Commission of the UIAA, the International Climbing and Mountaineering Federation, puts a number on the pace it considers sensible for children: an ascent rate of 300 m per day above a 2,500 m sleeping altitude, with a rest day every 1,000 m gained. Essentially no Colorado ski holiday itinerary respects that, and the ones the resorts sell do not either. We are not telling you to respect it either. We are telling you that when your child has a headache at 8pm on arrival day, this is the reason, and it is not because you did something reckless.

Notice how the UIAA guidance is written. It is not phrased as a limit on how high your child can ski for a few hours. It is phrased as a limit on sleep altitude.

The UIAA's consensus statement on children at altitude says, with an explicit caveat that there are no scientific data behind the figure, that it is generally recommended not to ascend to a sleep altitude higher than 3,000 to 4,000 m with a preschool child, and to prefer a sleep altitude below 2,500 m.

2,500 m is about 8,200 ft. Here is the fact that does not appear in any resort brochure: all four of the resorts in the table below are above it, before you take a single lift.

That does not put these resorts off limits for a 4 year old, and the UIAA does not say it does. Its firmer ceiling, the 3,000 to 4,000 m one, sits comfortably above every Colorado base in this guide. What it means is that when you take a preschooler to Breckenridge, you are sleeping above the altitude the guidance prefers, and the way you buy that back is with time and with where you sleep on night one. Not with a different lift ticket.

One time-sensitivity flag. That UIAA statement was published in 2008. As of 2026 the UIAA's own working group has been preparing an updated version, which had not been published when we compiled this guide. It is the current official guidance, not the last word, and it is worth re-checking if you are reading this a season or two from now.

Winter Park's 9,000 ft base is published on the resort's own mountain-statistics page, and we read it there. The Breckenridge, Keystone and Copper Mountain figures are the widely published base elevations, cross-checked across several independent sources, but none of the three came to us first-hand from the resort.

Being precise about that, because this is the section where precision is the whole point: Breckenridge's and Keystone's own pages blocked automated access when we tried them. We did not attempt Copper Mountain's at all, having already been blocked repeatedly on the two other resort sites we tried. So that is two checked and blocked, and one not checked. The numbers are stable and identical everywhere they appear, and we would rather tell you how we know than let you assume.

This is the part parents actually need, because a 3 year old does not say "I have a headache and it is worse when I bend over."

The UIAA is blunt about it: "Young children are not reliable reporters of symptoms, even when they can talk." It adds that children roughly aged 3 to 8, and children with learning or communication difficulties, may also be poor at describing their symptoms, which makes altitude illness hard to recognize. From age 8 up, it assumes altitude illness presents much the way it does in adults.

So the CDC lists what to watch for instead, in children too young to talk: loss of appetite or irritability, unexplained fussiness, and changes in sleep and activity patterns. Older children may complain of headache or shortness of breath.

Translate that into an evening in a Colorado condo. Your child will not eat a dinner they would normally inhale. Your child is crying about things that are not usually worth crying about. Your child falls asleep on the sofa at 5.30pm and never does that, or cannot settle at all. Your child has gone quiet and still. Writing about how badly young children communicate physical discomfort in the mountains generally, the UIAA notes they are unlikely to announce it and would probably just become very quiet and still.

Real talk: every one of those also describes a child after a 5am airport start. That overlap is exactly why the 1993 study found 21% of sea-level children reporting three or more of the same symptoms. You are not expected to tell them apart on night one. You are expected to keep watching, and to know what moves this into a different category.

Vomiting deserves its own line, because parents ask about it constantly and because it cuts both ways. A child can vomit at altitude for reasons that have nothing to do with altitude: the switchbacks on the drive up, a bug picked up in an airport, too much sugar at 4pm. We are not going to tell you which it is. What we will tell you is that repeated vomiting in a child at 9,000 ft is the point where "watch and see" stops being the right plan and calling someone starts being the right plan. That is a threshold for action, not a diagnosis.

Those red flags come from the general altitude-illness literature, which is written mostly around adults and older children, rather than from a pediatric-specific checklist we can cite line by line. That is a real limitation and you should know about it. We have written them as prompts to pick up a phone, not as a tool for diagnosing your child at 11pm.

If you are reading this section because your child is unwell right now, stop reading and call someone.

Descent is the thing altitude medicine agrees on. Two ideas sit underneath almost everything written on the subject: do not go higher while symptoms are unresolved, and going down is what makes altitude illness better. We are stating those in our own words, as widely held practice rather than as a quotation from any particular guideline, because we did not source them line by line from the CDC, the UIAA or the Wilderness Medical Society. And we are not putting a metre figure on how far down, because that threshold belongs in a clinical guideline and in a conversation with a doctor, not in a family travel article.

Here is where Colorado gets awkward, and it is the operational detail almost nobody flags. At plenty of Alpine ski areas, going down is a lift ride, because the village sits below the slopes. At Breckenridge, Keystone and Copper Mountain, the base village is your accommodation, so descending is not something you do on a chairlift. It is something you do in a car. The nearby Summit County towns of Frisco, Dillon and Silverthorne sit below the resort bases, but only modestly, so a short drive down I-70 buys you a few hundred feet rather than a different world. Going meaningfully lower means driving on toward the Front Range, which at 10pm in February is a real decision rather than a lift ride. Winter Park is in Grand County rather than Summit, so that particular geography is not its geography, but the principle holds there too: descent is a drive, not a lift.

The practical consequence: work out your descent option before you need it, not during. Know whether the booking is cancellable, know how long the drive down is, and understand that "we will just see how tonight goes" is a plan that works fine almost every time and is very hard to execute at 2am on the one occasion it does not.

Pro tip: if you are traveling with a preschooler and you have any choice in the matter, spend the first night lower and drive up the next morning. Denver's nickname, the Mile High City, is about right, and the base villages in the table above sit closer to 1.8 miles up. It costs you half a ski day, and it moves the hardest night, the one straight off an aircraft, to the lowest sleeping altitude of your trip. This is not the multi-day acclimatization the CDC describes, and we are not going to pretend it is. It is the version a family with one week of holiday can actually execute.

Somewhere in your search results, a page has told you the milligrams. Do not use that number.

The Wilderness Medical Society updated its altitude illness clinical practice guidelines in 2024, and the pediatric acetazolamide dose changed in that update. A large amount of web content, including content that looks authoritative and carries no visible date, still circulates the older figure. We are not publishing a dose here at all, in either direction. Dosing a child is a doctor's decision, and the fact that the reference figure moved this recently is the clearest possible argument for getting it from a clinician rather than from a page like this one.

Two things are worth knowing before you even have that conversation.

First, the CDC states that acetazolamide is not approved for altitude illness in children under 12, although it is used in children for other indications.

Second, the UIAA is unusually direct for a consensus document: drug prophylaxis to aid acclimatization in childhood should be strictly avoided, because there are no data or experience behind it. Slower ascent, it says, achieves the same effect in most cases. It allows one narrow exception, where a rapid ascent is truly unavoidable, and even then only after medical advice and with doses adjusted to body weight.

Now read that in the context of a ski holiday. A ski holiday is not an unavoidable rapid ascent. It is a discretionary one. That does not make it wrong to take, and we are not suggesting it is. It does mean the pill is not the family ski trip's altitude plan, and that if you want a prescription conversation, you have it with your own doctor weeks before you fly rather than with a pharmacy in a resort village.

Three reassurances, offered because this kind of article usually only ever tells you to be more careful.

The elevation gap between these four resorts is the smallest lever you have. The spread from Winter Park's base to Copper Mountain's is about 712 ft, roughly 220 m. That is real, and if you are choosing between them on other grounds anyway then by all means take the lower one. But it is small next to the sea-level-to-9,000 ft jump you are making regardless. Picking Copper over Winter Park is not the decision that determines how your child's first night goes. The shape of your first 48 hours is.

Mild symptoms on the first evening are not evidence that you made a bad call. The CDC describes acute acclimatization as a 3 to 5 day process. A headache and an abandoned dinner on night one, better by night two, is that process working rather than failing.

You do not need a medication plan to be a responsible parent here. The most authoritative pediatric statement we found on the subject, the UIAA's, actively discourages drug prophylaxis in children and points at slower ascent instead. For once the boring intervention is the recommended one.

If you are still choosing between resorts, our Colorado family resorts comparison and beginner-friendly Colorado shortlist cover the non-medical side, and the family ski trip checklist handles everything that is not about breathing.