Fine at Lunch, Limp by Dinner, and the Thermometer Won’t Say Which Bug

He ate a full sandwich at noon. By six he is flat on the couch with his cheek on a cushion, hot to the touch, telling you his legs hurt. You find the thermometer, and it shows a number that could mean almost anything.

The two illnesses overlap more than you would like. A fever, a cough and a stuffy nose can belong to either one. The number tells you little. How it started and how sick he looks tell you a lot more.

How do you tell the flu from a cold in a toddler?

Start with the clock. The American Academy of Pediatrics (AAP) lists a sudden fever, usually above 100.4°F, among the flu’s symptoms, along with chills, a headache, body aches and being a lot more tired than usual.

A toddler can’t say her body aches. You see it instead. She stops playing, drops the toy she begged for, and wants to be held flat against you.

• Fever: the flu tends to bring a sudden one, while a cold usually brings only a low-grade fever.
• Nose and cough: a cold usually means a runny nose and only a small amount of coughing. The flu adds a dry, hacking cough.
• Stomach: some children with the flu throw up or have loose stools. If vomiting rules the night, see our guide to stomach bugs in toddlers.

None of these rows is a rule. The AAP’s own list of cold symptoms includes fever, cough, fatigue, a stuffy nose and a sore throat, so a fever by itself tells you little.

Watch how she acts instead. How far is she from her normal Saturday-morning self? That gap is your best tiebreaker at home.

How long does each one last?

Neither runs on a short clock. The flu can last a week or even longer, the AAP says, and healthy children usually get over it in about a week. After the first few days, a sore throat, a stuffy nose and a continuing cough become the most obvious symptoms.

For a cold, the advice is to report back to your pediatrician if symptoms are not getting better each day, or are not all better after one week.

The slope matters more than the calendar. A cold that eases a little each day is behaving like a cold. A child who seems better and then gets worse again is a different story.

Can you tell flu, a cold and COVID apart at home?

Not reliably. The AAP says some symptoms of the flu, COVID and other respiratory illnesses are similar, and that your child’s pediatrician may order a test if it is necessary to confirm a diagnosis.

The same page adds two things. Children can have the flu and COVID at the same time, and a second illness, such as pneumonia or an ear infection, can follow the first. If a cough hangs on for weeks, our guide to walking pneumonia in kids covers what to watch for.

RSV shares many of the same symptoms, and our guide to RSV in toddlers covers its breathing signs.

Why bother? For the flu, timing matters. Antiviral medicine works best when it starts within the first one to two days of showing signs, and your pediatrician decides who gets it.

Why does the flu matter more for kids under 5?

Colds are the background noise of childhood. Healthy children get about 6 to 10 of them a year, the AAP says. If your house seems to catch every one, our post on why kids get sick so often explains why.

The flu is a different animal. Any child can develop severe, life-threatening influenza. The AAP also names children younger than 5, especially those younger than 2, among the kids whose parents should call the pediatrician within 24 hours of the first flu symptom to ask about antiviral medicine.

Vaccination is the best way to prevent it. The academy recommends a flu vaccine every year for everyone age 6 months and older, and it calls the shot especially important for children from 6 months to 5 years old. Protection takes about two weeks to build, so the timing matters: as soon as it is available, ideally by the end of October.

When is it a phone call, and when do you go in right now?

The AAP says to let your pediatrician know if a fever lasts more than 3 days or goes away for 24 hours and then comes back. Ear pain, sinus pain, and pressure in the face and head belong on that list, along with a cough and fever that will not go away. Toddlers can’t say which ear hurts, so see our guide to an ear infection after a cold.

If your child has the flu and any of these show up, the AAP says to contact your pediatrician or seek immediate medical care:

• Trouble breathing or unusually rapid breathing
• Pale, gray or blue-colored skin, lips or nail beds
• Ribs that pull in with each breath
• Chest pain
• Muscle pain so severe that your child refuses to walk
• No peeing for 8 hours, a dry mouth, and no tears when crying
• Not alert or interacting with you while awake
• Seizures
• A fever above 104°F
• Any fever in a child younger than 12 weeks
• A fever or cough that seems to improve but then returns or worsens
• A chronic condition, such as asthma, getting worse

You will not always know which illness you have. The advice for those nights is short: if you have questions or concerns about your child’s symptoms, don’t hesitate to call your pediatrician. A seal-bark cough has a name, and our croup guide covers the first ten minutes.

What about cold and flu medicine for kids?

Read the shelf label first. The AAP says over-the-counter cough and cold medicines “should NOT be given to infants and children under 4 years of age because of the risk of dangerous side effects.” It adds that several studies show these products, taken by mouth, do not work in children younger than 6.

What is left is unglamorous. Extra rest, plenty of water or other liquids, and saline nose drops make a child comfortable, which is the best treatment a cold gets. Antibiotics have no effect on the viruses behind a cold or the flu.

Check the cabinet too. Many cold medicines already contain acetaminophen, so giving one alongside a fever medicine can mean a double dose.

Before the next fever, save one number in your phone

Ask your pediatrician’s office if it has an after-hours line, and save that number under a name you could find half asleep. Do it while nobody is sick. Then put a second set of pajamas within reach of the bed, because you will be glad of both at 2 a.m.