The measures taken to treat a fever in children will vary by age and how long the child has had a fever. According to Dr. Stovall, newborns (babies younger than 3 months) with a rectal temperature of 100.4 degrees Fahrenheit will need to see a doctor the same day. Children ages 3 months to 3 years with a rectal temperature of 100.4 or greater for three days or more accompanied by illness symptoms should also see a doctor.  According to Dr. Patilla, oral, rectal, or forehead temperatures of 104 degrees Fahrenheit or greater, or axillary temperature of 103 degrees Fahrenheit or higher, are cause for concern. You should contact your pediatrician immediately. Typically, a fever isn’t dangerous for most healthy kids acting well, Dr. Pitone says. She explains that a fever is the body’s way of helping the immune system fight off an infection. Overall, how your baby appears clinically is more concerning than the number on the thermometer. According to Dr. Amin, a good thermometer helps monitor the duration of the fever, but your child’s doctor is more concerned with how your child is acting than the number.