A toddler has a fever when their rectal temperature reaches 100.4°F (38°C) or higher. That’s the standard threshold used by pediatricians, but the exact number depends on how you take the temperature. An oral reading of 100°F or higher, or an armpit reading of 99°F or higher, also qualifies as a fever.
Fever Thresholds by Thermometer Type
Your toddler’s temperature reading will vary depending on where you measure it. These are the cutoffs that indicate a fever:
- Rectal, ear, or forehead (temporal artery): 100.4°F (38°C) or higher
- Oral (under the tongue): 100°F (37.8°C) or higher
- Armpit (axillary): 99°F (37.2°C) or higher
These numbers aren’t interchangeable. A rectal thermometer measures core body temperature, which runs slightly higher than what you’d get from the mouth or armpit. If you take an armpit reading, you’ll generally need to add half a degree to a full degree Fahrenheit to estimate what the core temperature actually is.
Which Thermometer Is Most Accurate
For children 3 and younger, a rectal thermometer gives the most accurate reading with a standard digital thermometer. It’s not the most pleasant option, but it’s the one pediatricians trust most for this age group. Digital ear thermometers work best for children between 6 months and 1 year, though they’re slightly less precise than rectal readings.
Armpit readings are the least accurate because they measure skin surface temperature rather than internal body heat. Most armpit tissue isn’t close enough to major blood vessels to reflect what’s happening inside. Forehead strip thermometers are even less reliable. Research from the University of Oxford found that these strips miss 4 out of every 10 fevers, making them a poor choice when accuracy matters.
Normal Temperature Fluctuates Throughout the Day
A toddler’s body temperature isn’t a fixed number. The average oral temperature for children 2 and older is about 98.6°F, while rectal averages sit closer to 99.3°F. But healthy children can swing nearly 2°F over the course of a single day. Body temperature bottoms out around 6 a.m. and peaks between 4 and 6 p.m., which means a reading taken in the late afternoon will naturally run higher than one taken in the morning.
This matters because a temperature of 99.5°F at bedtime might be completely normal, while the same reading first thing in the morning could be more meaningful. Some studies have found that normal temperatures in young children can reach 100°F without any illness present, especially in the evening hours.
Why Fevers Happen
Fever is not an illness. It’s your toddler’s immune system responding to an infection, most commonly a virus. When the body detects an invader, immune cells release signaling proteins that travel to the brain’s temperature control center and raise the internal thermostat.
This temperature increase actually helps fight off the infection in several ways. Higher body heat slows the growth and reproduction of many bacteria and viruses. It also reduces the amount of iron circulating in the blood, which matters because many bacteria need extra iron at higher temperatures to survive. At the same time, fever ramps up the activity of white blood cells and boosts the production of infection-fighting proteins. In short, a low-grade fever is your toddler’s body doing exactly what it’s designed to do.
Comfort Measures at Home
A toddler with a mild fever who is still playing, drinking, and acting mostly like themselves often doesn’t need medication right away. Focus on keeping them comfortable. Offer plenty of fluids, including water and electrolyte drinks like Pedialyte. Eating is less important in the short term, but staying hydrated is essential for a sick child. Dress your toddler in lightweight clothing rather than bundling them up, and a cool washcloth on the forehead can help if their skin feels hot.
Avoid ice baths, which can cause significant discomfort and aren’t recommended. Alcohol rubs are also unsafe for children.
If your toddler seems uncomfortable or isn’t sleeping well because of the fever, acetaminophen (Tylenol) can be given every 4 hours, and ibuprofen (Motrin) every 6 hours. Ibuprofen is approved for children 6 months and older. Both are dosed by weight, not age, so check the packaging carefully or ask your pediatrician for the right amount. Never give aspirin to a child.
When a Fever Needs Medical Attention
The number on the thermometer matters less than how your toddler is acting. A child with a 102°F fever who is drinking fluids and playing may need nothing more than monitoring, while a child with a 101°F fever who is limp, unresponsive, or difficult to wake warrants a call to your pediatrician.
That said, certain situations call for prompt medical contact:
- Temperature above 104°F (40°C) repeatedly in a child of any age
- Fever lasting more than 24 hours in a child under 2 years
- Fever lasting more than 3 days in a child 2 or older
- Accompanying symptoms like a stiff neck, severe headache, difficulty breathing, an unexplained rash, or repeated vomiting or diarrhea
- A seizure during the fever
- Your child still seems sick after the fever comes down with medication
Children with immune system conditions, heart problems, or those taking medications that suppress the immune system should be evaluated sooner rather than later when a fever develops.
Febrile Seizures
Some toddlers experience seizures triggered by fever, called febrile seizures. These are more common than most parents expect and occur in children between about 6 months and 5 years old. A simple febrile seizure lasts a few seconds to 15 minutes and happens only once within a 24-hour period. It involves the whole body rather than just one side.
Complex febrile seizures last longer than 15 minutes, occur more than once in a day, or affect only one part of the body. These need medical evaluation. Prolonged febrile seizures lasting more than 30 minutes carry a small risk of developing into epilepsy later, but simple febrile seizures do not cause brain damage and most children outgrow them entirely. If your toddler has a seizure with a fever, lay them on their side, don’t put anything in their mouth, and contact your pediatrician afterward.