This depends on the age of the child. Any infant less than 28 days old with a fever of 100.4F (38C) should be evaluated right away. Between one and six months old, a temperature of 100.7 or higher should be discussed with the child’s healthcare professional. Meanwhile, for older, fully immunized children, a temperature of 102.2 and above indicates it’s time to call the doctor.
But even if your kid’s fever is below that threshold, there are plenty of measures you can take at home to remedy the situation–a cool compress on their head, bathing them in lukewarm water and making sure they’re getting plenty of liquids, as well as fever reducers such as acetaminophen and ibuprofen.
In general, for children older than about 2 years old, we often follow the practice of “treat the child, not the number.” I’ve seen plenty of kids acting playful and smiling with a temperature of 102 and an equal number feeling crummy at 100. As always, if you have any concern about how your child is acting regardless of temperature, check in with your healthcare professional.