She's become something of an expert in detecting the symptoms  -- especially the most obvious one. "I can always tell when one of my kids has an earache," says Dover, of Carmichael, CA. "That child cries all night."

It's a cry that most parents of young children quickly learn to interpret: Next to colds, middle-ear infections (called otitis media) are the most frequently cited reason for visits to the doctor. Seventy-one percent of children have at least one incident by the age of 3, and 46 percent have at least three.

Typically, a middle-ear infection sets in after a cold has been raging for at least two or three days. Normally, the middle-ear cavity produces small amounts of fluid that usually drains out through the eustachian tube, which connects the middle ear to the back of the nose. When the eustachian tube becomes swollen because of a cold, sinus infection, or allergy and stops functioning properly, fluid begins to accumulate.

Otitis media actually comes in two forms: otitis media with effusion (OME), where there is fluid in the middle-ear canal but no signs of acute infection; and acute otitis media (AOM), where there is both fluid and a bacterial or viral infection that causes inflammation and pain (see page 85 for the differences between the two).

The fluid accumulation and the resulting pressure on the eardrum can cause anything from discomfort and temporary hearing loss to extreme pain. For parents of children who've never before been through either form of middle-ear infection, however, it can be difficult to figure out what's wrong, especially if their child isn't talking yet. But there are several symptoms to look for, and if you see any of them, you should call the doctor.

• Loss of appetite and sleeplessness.

• The desire to be held more than usual.

• Yellow or white discharge from the ear, caused by a tiny rupture in the eardrum.

• A fever ranging from 100 to 104 degrees, but only in a child suffering from AOM.

• Ear tugging, though this isn't as common a clue as many people believe; but if your child is constantly poking his finger into his ear or shaking his head, that may indicate a problem.

• Some loss of hearing, although in most cases it gradually returns to normal after the infection subsides. If your child keeps asking you to repeat what you just said, that could be a sign. With babies, it's more difficult to tell and potentially more worrisome, since hearing loss could affect your baby's language development. If you suspect a problem, have your child's hearing checked with an audiometer.

Benjamin Spock, M.D., is a contributing editor and the author of Dr. Spock's Baby and Child Care.