. Taking baby's temperature. Sleeping 7-month-old baby girl lies with a mercury thermometer in her armpit. Her temperature can be read using the scale running along the thermometer. An armpit temperature above 36.8 degrees Celsius would indicate that the baby has a fever, although temperatures vary with time and from person to person. Most fevers are caused by bacterial or viral infections. Symptoms include shivering, sweating, hot skin and thirst. MODEL RELEASED