A good rule of thumb is simply to dress your baby as warmly or lightly as you're dressed for the weather. If you're warm enough in a t-shirt, that's all he'll need, too. Young babies are particularly sensitive to the sun. Don't forget a hat when you're outdoors.

Dressing for warm weather
For warm weather, your baby's clothing should be lightweight and should breathe (choose cotton instead of 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 before he is six months of age. After that age, 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 10:00 a.m. and 3:00 p.m.

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 she wears a sun hat and that her 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.

Dressing for 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 her up more. If she's very quiet or listless, or if she feels hot or sweaty, she's too warm.