Fever is one of the prime reasons that parents call their children's doctors, and it is true that any fever in an infant younger than 3 months is cause for major concern, as there is a risk of serious bacterial infections. Also, a child who has a seizure with fever should be checked by a physician, at least the first time.
However, fever is actually a signal that an immune system is working well and in older children who do not appear to be particularly distressed, fever is a positive sign. It is evidence that the child has an active immune system. Fever does not harm your brain or your body, although it does increase your need for fluids.
Parents are not the only people who may become overly concerned, however, according to the New York Times:
"Other studies have looked at attitudes among medical personnel, who can be just as worried about fever as parents ... Some of the phobia 'comes from doctors and nurses.'"