Fever is nothing to fool around with in young children. If your child feels warm or seems under the weather, you probably should take his or her temperature. Sounds simple enough, but if you're new to it, you probably have a few questions. What kind of thermometer should you use? Should you take a baby's temperature the same way you take the temperature of a five-year-old? Here are the answers.

If you grew up before the 1980s, your parents probably took your temperature with a glass thermometer — a skinny tube with a narrow, rounded tip containing mercury. Glass thermometers are becoming scarce these days because the mercury they contain creates health and environmental risks. Since 2001, the American Academy of Pediatrics has recommended against the use of glass thermometers.

But you can still choose among many types of thermometers. Thermometers with newer designs, in fact, are easier to use and to read than glass thermometers. And, all the better for your child, they give you a very quick result.

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Choosing a thermometer

The best method depends on the child's age.

• Newborns. For babies less than 3 months old, start with an armpit (axillary) temperature. If it's higher than 99 F (37.2 C), take a second measurement rectally. A rectal measurement of temperature is more accurate than an axillary measurement. Rectal temperatures higher than 100.5 F in infants require immediate medical attention.
• 3 months old to 4 years old. For this age group, doctors recommend using a rectal thermometer or an electronic pacifier thermometer. For children 3 months or older, an ear thermometer can be used.
• Five years and older. After age 4, most children are able to hold an oral digital thermometer under the tongue for the short time it takes to get a temperature reading. Once children start school, doctors say it's preferable to take their temperature by mouth.

Instructions vary depending on the type of thermometer and the method you use — oral, rectal, axillary or ear. One safety rule applies to all methods and thermometers: Don't leave your child unattended with a thermometer in his or her mouth, armpit or rectum. Similarly, you — not your child — should insert an ear thermometer and hold it in place.

For step-by-step instructions, see:

Although your child's high temperature may worry you, most children tolerate fevers amazingly well. Low-grade fevers may actually help the body rid itself of viral infections. If your child is responding to you normally, drinking fluids and continuing to play, there's probably nothing to worry about.

On the other hand, if your child is listless, vomiting persistently, or complaining of a headache or stomachache, contact the doctor or go to an emergency department immediately. Also seek medical attention if your child's fever does not respond to fever-reducing medication or if a febrile seizure occurs.