Here's some great, in depth information on winter wear for infants. I found it on a network on facebook. It talks about everything you'd need to know. I recommend that all mom's and dad's read it. Even though it's super long! I promise it will be worth it!
Layers: This is the most important principle for enthusiasts of any age. The colder the weather, the more layers needed. Your baby will generally need more layers than you will, since he or she is not as active, therefore not producing as much heat. Start with one-piece undershirts and work your way outward. Synthetics like fleece are better than cotton, which is deadly when wet. For really cold days, be sure the outermost layer is wind- and waterproof or water-resistant. A snowsuit with a nylon shell and a heat-generating inner layer like fleece or wool (stack layers so that itchy wool won't irritate your baby's skin) should do the trick. (See discussion board regarding choosing a baby snowsuit.)
Heads: Humans lose more heat through their heads than anywhere else. This is especially true for babies, who have proportionately bigger heads than adults. This translates into hats, hats, and more hats. Don't be afraid to use more than one hat, and hats inside hoods. For infants, always keep heads and faces protected, but be sure they can breathe! Cozy-fitting fleece hats with earflaps protect the head, ears, and much of the neck. Velcro straps at the bottom of the hat are always a help keeping them on. This sort of hat makes a great combo with a hooded snowsuit. The fleece provides a warmth layer while the snowsuit helps keep out any wind.
Hands, feet, and legs: All of these extremities are places where the body loses heat fast. For babies, use snowsuits and fleece coveralls that have coverings instead of openings for the hands and feet. Under the one-piece, use extra mittens, socks, tights, or long underwear in cold weather. You'll typically want something wind- and waterproof as the outermost layer, and remember that whatever you use, little boots aren't always warm and often come off easily.
Little legs: You and older children may feel great in a warm jacket, but babies and toddlers need extra layers on their legs since they don't move at all, or, in the case of toddlers, they don't move very fast. Don't forget to have extra layers on their legs, such as snowsuits, fleece, or wind pants. As part of the inner layering thick leotards or tights can help keep legs warm. Periodically check for any places where air might get to your baby, such as the face or hand or shoe openings of coats and pants. Make sure skin stays covered on cold days. Also keep track of runny noses, which can add to cold-weather discomfort.
Avoid the glare: Remember to protect your baby's eyes. Glare can be especially bad on snow, so consider a pair of sunglasses or UV-protective goggles for your tot.
Front packs: Front packs provide more of your own body heat and natural protection to your child than do backpacks. When using a front pack, it's easier to keep a baby's face protected from the wind, since he's facing you. Another advantage to using front packs is that you can actually see your child. If you do use a backpack it will be helpful to have another person present to check that your child is happy and warm.
Testing: It can often be tough. You can't ask a baby, after all, and you can't always depend on signals. Crying is helpful, of course, but cold babies don't always cry. Your child may even be sleeping through the cold. Periodically test your baby's warmth by touching his nose, cheeks, or fingers. Of course, to thoroughly check your child you sometimes need to expose him to the elements. How can you safely check on your child's foot or fingers for warmth if they're already well bundled up? You have to be very quick with your testing and minimize exposure, particularly if it's really cold or windy.
Always stay in familiar territory: The last thing you want to do is get lost with your infant on a cold day. And if your baby is fussy, turn back. This isn't the time to tough things out.
Keep outings short: The more you venture out and test layers in various temperatures, the better sense you'll have of your baby's cold-weather needs.
At the end of each adventure, as you unbundle your child in indoors warmth, immediately test his hands and feet, particularly to see if he's been dry and warm. This is the test of whether your outing has been successful and will give you clues to what may be needed on your next winter trip.
