Just cover as much of the body as possible. This can lead to dehydration. Be sure that the child is getting plenty of fluids. Altitude sickness is common in Yellowstone. It is due to differences in pressure and air thickness at higher altitudes.
Common symptoms are dizziness, nausea, restless sleep, sore throat, and shortness of breath.
Be sure to take prcautions for this if your baby has asthma. Also, if you notice that your baby seems to be experiencing discomfort, this might be the problem. Altitude sickness tends to go away after a few days. The following are a few suggestion about hiking with kids provided by Sunflower. I've jotted down a few things that have made our hiking trips with our kids a lot of fun.