Avoid going out if the temperature is below freezing or above 80 degrees. Shield your baby from wind, rain, snow, and direct sunlight. Wherever you're headed, plan for the weather. A good rule of thumb is simply to dress your baby as warmly or lightly as you're dressed. If you're warm enough in a t-shirt, that's all he'll need, too—even tiny babies don't need heavy blankets on a hot day. If you dress your baby in light layers you'll be prepared for changes in temperature. Feel the skin on torso, arms, or the back of baby's neck. If he seems cool, add a layer; if he's sweating, take one off. Remember, young babies are particularly sensitive to the sun. Don't forget a hat when baby is outdoors.

For warm weather, your baby's clothing should be lightweight and should breathe (cotton as opposed to nylon). Light colors will reflect sunlight and keep your baby cooler. Dress your baby in light-colored, lightweight cotton pants, a long-sleeved top, and a wide-brimmed hat or bonnet for protection. When you go from the hot outdoors to an air-conditioned room, cover baby lightly with a sweater or blanket to protect against getting chilled.

Check with your pediatrician before using sunscreen on your baby earlier than six months of age. After that, be sure to put sunscreen on any time baby will be exposed to sun; consult your physician about what kind to use. No matter what baby's age is, avoid the summer sun between 10 a.m. and 3 p.m.

Stay in the shade
Use a stroller hood or portable clamp-on umbrella when you walk with your baby on a sunny day. Any part of your baby that sticks out—arms or legs, for example—may get sunburned.

If you use a baby carrier, pay extra attention to how hot baby is getting. If your carrier is made of corduroy or other heavy material, your baby may become overheated. Be sure he wears a sun hat and that his arms and legs are covered. Check her neck, back, or chest to be sure that she isn't getting sunburned.

Like you, your baby should drink extra liquids in hot weather. Water, diluted juice, or breast milk are good choices. Avoid sports drinks, which are full of sugar and salt.

What to do in cold weather
For many people, wrapping a baby in blankets and sweaters seems to come naturally. Follow the same rule in cold weather as in hot: let your own comfort level be the guide. Dress your baby in as many layers as you need to stay warm. Put a hat on baby whenever it's chilly. A hat with a visor worn over a warm cap will protect from the midday sun. In addition, protect your baby from rain, snow or strong wind.

Be sure not to overdo the blankets, however, when the temperatures drop. If you are in a house or heated car wearing only a shirt and a jacket, don't wrap your baby in six or seven layers. She'll be too hot.

If your baby complains or feels cold, bundle him up more. If he's very quiet or listless, or if he feels hot or sweaty, he's too warm.