I encourage taking your baby to Yellowstone as soon as possible. My first trip to Yellowstone was when I was 8 months old and I thank my parents for it every day. There are just a few things that you have to remember when traveling with a baby in an area like Yellowstone.
The sun can mean trouble for your child's health if they are not protected from it. Also, dealing with a sunburned baby for the rest of your trip cannot be too pleasant. Besure to cover up as much of their skin as possible with outfits made of light fabric (so that they don't get too hot). A hat is always a good idea, too. Don't use sunscreen until you are sure the baby is old enough to wear it without the chemicals in it being dangerous.
At certain times of the year, biting bugs in Yellowstone can get very nasty!! I know how I get when I get bug bites, so I can just imagine how a baby would be! The precautions for this are similar to those for protecting them from the sun. Just cover as much of the body as possible. Again, don't use a bug spray until you know that the child is old enough to handle the chemicals without harm (especially dangerous for babies who fut their hands in their mouths a lot).
There is practically no humidity in Yellowstone so it might appear that your child is not sweating (due to the fact that sweat evaporates immediatly). But, if it is hot, they are sweating! This can lead to dehydration. Be sure that the child is getting plenty of fluids. This might lead to more diaper changes, but at least your baby will be safe!
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. There might be a cure that I don't about (please recommend one to me if you do), but, if you know it is happening, just take it slow. Altitude sickness tends to go away after a few days.
Hiking
The following are a few suggestion about hiking with kids provided by Sunflower. Thanks Sunflower!!
ESSENTIALS
Always keep a close eye on the kids, don't approach the wildlife and
always keep a hand on them in thermal areas.
Seeing Yellowstone through a child's eyes is truly a wonderful thing.
I've jotted down a few things that have made our hiking trips with our
kids a lot of fun. Feel free to use some, all or none of them.
Games
THE HIKE
My kids favorite hikes are Lone Star and Storm Point.
Some teens you will find already have a great affinity for the outdoors and they are eager to take a trip to Yellowstone. You should have no problem traveling with these teens!Remember that teenagers are teenagers and all might not be interested in the Yellowstone experience. I was recently a teenager and remember the times when music, movies, members of the opposite sex, and various other things occupied a good majority of my intrests at all times. Some teens might not find a week long adventure with the family to be that exciting of an experience in the tumultuous world of their teenage lives. Be sure that you play off of their intrests when traveling. If you discover somthing that does intrest them, encourage it even if it doesn't fit in with the rest of the plans for your trip. I think that you will find that every teen has a soft spot for the outdoors and will end up greatly enjoying the experience!