The K Health Guide to Common Childhood Illnesses

By Howard Jeffries, MD
Medically reviewed checkmarkMedically reviewed
February 10, 2020

Children can get sick frequently and as a parent, you may be worried about the seriousness of your child’s medical condition. It’s important to know what illnesses your child may encounter, how to treat them, and most importantly, when you should see a doctor. While there are countless childhood illnesses and diseases, in this article I’ll provide an overview of the main ones to know about.

Viral vs. Bacterial Illnesses

Both viruses and bacteria are tiny organisms or microbes that can cause illnesses. These illnesses may be mild, moderate, or serious and can be acute (short-lived), chronic (long-lived), or even latent meaning they don’t cause symptoms at first but can reactivate months or years later. Both types of microbes can be easily spread through coughing and sneezing; contact with infected children; contact with contaminated surfaces, food, and water; or contact with infected animals, fleas, and ticks. They also can cause similar symptoms, such as coughing, sneezing, fever, inflammation, vomiting, diarrhea, fatigue, and cramping. These symptoms occur while your child’s immune system is fighting off the infection.

Bacterial illnesses

The differences between viral and bacterial illnesses are due to the microbes’ structural differences and the way they respond to medications. Bacteria exist everywhere and can be both beneficial; as in those which help absorb food in our intestines, destroy disease-causing microbes, fight cancer cells, and provide essential nutrients; and harmful, such as streptococcus that can cause illness. However, fewer than 1% of bacteria cause diseases in people and they can usually be treated with antibiotics.

Viral illnesses

Viruses are even tinier organisms that also exist everywhere but antibiotics are not effective against viruses. Antibiotics won’t work against viral infections and may even cause side effects such as diarrhea which will only make your child feel worse. To treat viral infections, your child will need to drink plenty of fluids and rest. It may take some time for their immune system to fight off the virus.

Viral illnesses are more common than bacterial infections and will account for most of your child’s illnesses. Unfortunately, they are usually very contagious and can be easily passed to other members of the family. Occasionally, if your child has a viral illness, he or she can be more susceptible to getting a bacterial infection. These include, for example, ear infections, pneumonia, or sinus infections. This may be the case if your child’s symptoms are persisting longer than the normal 10-14 days a virus is expected to last, their fever is higher than is typical for a virus, or their fever gets worse rather than improving after a few days. Your child’s pediatrician will likely prescribe an antibiotic to treat the bacterial infection while his or her immune system fights off the original viral infection.

List of Common Childhood Diseases

Thanks to widespread vaccination, many of the potentially serious childhood diseases are now rare in the Western world. Countless and robust evidence shows the importance of vaccinating your children. Unfortunately, whenever there is a drop in the number of people vaccinating their children due to misconceptions about their effectiveness and safety, the incidences of these childhood diseases increases leading to sometimes fatal consequences.

Below is a list of the most common childhood illnesses. Continue reading for brief descriptions of the following:

Upper respiratory infection

An upper respiratory infection (URI) is an inflammation of the nasal passages and large breathing tubes (bronchi) in the lungs. 90% of the time it is caused by a viral infection from a cold or flu but may also be caused by bacteria, dust, allergens, strong fumes, or cigarette smoke. The most common symptoms include a dry or wet cough, vomiting after coughing, runny nose, ear discomfort, chest congestion, slight fever, muscle pain, wheezing, and sore throat. These symptoms normally last 10-14 days but your child’s cough may continue for 3-4 weeks. If nasal symptoms persist with fever, sinusitis should be considered. Development of pneumonia is uncommon, but should be considered if a fever returns associated with a continued cough.

Chicken pox

Chicken pox is also known as varicella because it is caused by the varicella zoster virus. It is a highly contagious airborne disease that is characterized by a skin rash. This rash forms small, itchy blisters initially over the chest, back and face, before spreading to the rest of the body and eventually scabbing over. Symptoms begin 10-21 days after exposure to the virus and usually last 4-7 days. Typically, the classic rash occurs within one day after fever, sore throat, tiredness and loss of appetite begin. The varicella vaccine protects 70-90% of people so that more than 3.5 million cases of varicella, 9,000 hospitalizations, and 100 deaths are prevented each year in the United States.


Croup is a common respiratory infection, also known as laryngotracheobronchitis, affecting 3% of American children each year typically between the ages of six months and three years. It is more common in boys than girls and is usually caused by a virus (such as parainfluenza or adenovirus). Your child may find it hard to breathe and have the classic symptoms of a ‘barking’ cough, a high-pitched wheeze, and a hoarse voice due to swelling inside their windpipe (trachea). He or she may also have a fever and runny nose. Croup usually lasts less than a week and your child will be contagious for three days after symptoms start or until their fever has gone. The symptoms are usually mild and are often worse at night. Most children do not need to see a doctor, but croup can be very serious. Your child needs to see a doctor immediately if he or she starts to turn blue or looks pale, has a hard time breathing, can’t speak or cry, and is not responding to you.

Ear infections

Five out of six children will have at least one ear infection before they are three years old. It is the most common reason parents bring their child to the doctor. An ear infection, or otitis media, is a bacterial or viral infection that causes an inflammation of the middle ear and fluid build-up behind the eardrum.

Children with a painful infected ear may:

  • Tug or pull at their ear
  • Have trouble sleeping
  • Have a fever
  • Be clumsy or have problems with balance
  • Have fluid draining from their ear
  • Find it hard to hear quiet sounds

Fifth disease

Fifth disease is so-named because it is one of the six most common viral childhood illnesses with a rash. It commonly occurs in children who are 5-15 years old. Its medical name is erythema infectiosum and it is caused by a parvoviral infection. The symptoms usually start 14 days after infection with a low-grade fever, headache, and cold-like symptoms such as a runny or stuffy nose. Your child will then get a bright red rash a few days later usually on the cheeks of the face. He or she may also develop a red, lacy rash on the rest of their body, especially their upper arms, torso, and legs. Once the rash develops they are no longer contagious.


The flu is an airborne infectious illness with mild to severe symptoms caused by influenza virus. The most common symptoms include a high fever, runny nose, sore throat, muscle and joint pain, headache, coughing, diarrhea, vomiting, and tiredness. Symptoms normally start two days after exposure to the virus and last less than a week but your child may feel tired for three to four weeks. Some children may be more seriously affected and will need to be treated in a hospital, especially if a lung infection develops. It is recommended for all children older than six months to receive the influenza vaccine as many as two times a year to help protect against the flu and its potentially serious consequences.

Hand, foot, and mouth disease

This coxsackie viral infection is very contagious and normally occurs in children under five years old. It is characterized by painful blister-like mouth sores and a rash on the hands and feet. Other symptoms may include fever, sore throat, irritability, and loss of appetite which occur 3-6 days after catching the infection. The symptoms are usually mild and last for a few days.


Impetigo is the third most common skin infection in children, occurring most frequently in warm and humid environments. It is a bacterial infection that is highly contagious and is characterized by red sores on the face, especially around the nose and mouth, and on the hands and feet. These sores can then burst and develop honey-colored crusts. Your child will likely no longer be contagious once he or she has been on antibiotics for 24 hours. The antibiotics can be oral or topical depending on the extent of the infection.

Kawasaki disease

This childhood disease is the leading cause of acquired heart disease in American infants and young children since it can damage the heart muscle through injury to the coronary arteries. It mainly affects young children between six months and five years and those with Asian ancestry. Kawasaki disease has no known cause but is considered to be a reaction by the body’s immune system causing inflammation in a child’s blood vessels. Symptoms can be severe, including a high fever for several days, a rash, tender swollen neck glands, swollen hands and feet, and extremely red eyes, lips, and tongue. Peeling skin on the fingers and toes can occur 2-3 weeks after the fever starts. The good news is that children can recover in a few days with a low risk of long-term heart issues if the disease is recognized and treated within 10 days. Treatment consists of immune globulin intravenous (IVIG) and aspirin.


Measles is a highly contagious airborne infection caused by the rubeola virus. Symptoms usually develop 10-12 days after exposure to an infected person and last 7-10 days. Symptoms begin as a high fever, cough, runny nose, and inflamed eyes. About three days later, a child can develop small white spots (Koplik’s spots) inside their mouth and a red flat rash that typically begins on the face and then spreads to the rest of the body. Complications can be relatively mild, such as diarrhea, ear infections, and pneumonia but in severe cases, measles can lead to seizures, blindness, and brain inflammation. The measles vaccine is very effective and safe, is usually combined with other vaccines (MMR vaccine), and has dramatically reduced the number of measles-related deaths.


Meningitis is an inflammation of the meninges, which are the protective membranes covering the brain and spinal cord. Meningitis can be caused by both bacteria and viruses. Bacterial meningitis is rare but can be life-threatening if not promptly treated with intravenous antibiotics, while viral meningitis (also called aseptic meningitis) is more common but usually less serious and normally clears up within 7-10 days. Bacterial meningitis affects thousands of children each year in the United States, usually in young children under the age of five. The most common symptoms are fever, headache, and neck stiffness. Some forms of meningitis are preventable by immunization with the meningococcal vaccine (given at age 11-12), mumps, pneumococcal, and Hib vaccines.


Mumps is a very contagious viral illness that infects the pair of salivary glands in front of the ears. This childhood illness is now rare due to widespread immunization with the MMR (measles, mumps, and rubella) vaccine. Common symptoms include pain and swelling in the salivary glands, especially in the jaw area. Other symptoms include trouble talking and chewing, headache, earache, and fever. The most common complication is inflammation of the testicle in adolescent and young men resulting in testicular pain and swelling which usually results in hospitalization.

Pink eye

Pink eye, medically termed conjunctivitis, is a common contagious eye infection where there is an inflammation of the white part of the eye (the conjunctiva) and the inner eyelids. Pink eye is so-named due to the telltale red or pink color of the eye(s). Other symptoms can include itchiness, discomfort, and watery discharge from the eye(s). It is caused by bacteria and viruses that are also responsible for colds and other infections. It looks bad but is usually not serious.

Reye’s syndrome

Reye’s syndrome is a serious but extremely rare illness (fewer than 20 cases have been reported annually since 1988). Because it is so rare, little is known about the causes. It usually occurs in children who have had a recent viral infection, such as chicken pox or the flu. Taking aspirin to treat the headaches from these infections greatly increases the risk of Reye’s. It also occurs in children and teenagers who have a type of metabolic disorder that causes the body to be unable to break down fatty acids. Symptoms of Reye’s syndrome come on quickly and usually start with vomiting, followed by irritability or aggressiveness, then confusion and lethargy, and finally the possibility of seizures or a coma. Early treatment is needed to avoid brain damage.


Despite its name, this childhood illness is not caused by worms, but rather by a fungus. It is so-named because the infections on the scalp and skin grow and look like round spots surrounded by red scaly rings. They are mildly irritating and if on the scalp, your child may lose some hair in the area of the infection. Ringworm is contagious and can spread from sharing infected hats, brushes, and hair accessories. If not on the scalp, it can also be spread from infected pets. Treatment is usually through topical treatments including shampoos and creams.


Rotavirus is a contagious viral infection that causes nausea, vomiting, fever, and diarrhea. The diarrhea may last from 3-8 days and if severe, babies and children may become dehydrated and need hospital care. This childhood illness normally occurs between three months and three years of age. Rotavirus can be prevented by babies getting an oral vaccine.

Scarlet fever

Scarlet fever (or scarlatina) is a fairly rare childhood illness (less than 10 in 100,000 people get it each year). It can occur when a child has a strep throat or skin infection. The strep bacteria make a toxin that causes a bright red, bumpy, itchy, ‘sand-papery’ rash that begins in the groin and on the armpits and then spreads onto the rest of the body though usually spares the palms and soles. It normally begins to go away after about six days, but your child may have peeling skin for several weeks as the skin heals. Other symptoms include a fever, red sore throat, white covered tonsils and tongue, and swollen neck glands. Antibiotic treatment for the rash is the same as the treatment for the strep throat infection that led to scarlet fever.

Strep throat

Strep throat is a very common and contagious infection caused by group A streptococcus bacteria. It lasts only a few days with antibiotic treatment. Strep bacteria account for almost a third of all sore throats and mostly affects school-age children and teenagers. Other symptoms include fever, red and swollen tonsils, and painful or swollen neck glands. It is important to finish the course of antibiotics as that can reduce severe complications which include rheumatic heart disease and kidney problems.

Whooping cough

Whooping cough (or pertussis) is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis. It mainly affects babies younger than six months old who haven’t yet received the pertussis vaccine, and children 11-18 years old whose immunity has started to fade. It is so-named due to the severe coughing spells, which can sometimes end in a ‘whooping’ sound when the child breathes in. Such coughing spells can last for more than a minute, cause a child to turn red or purple, and may end in vomiting.

This childhood illness normally starts with symptoms similar to a common cold, and then after about 1-2 weeks, the dry, irritating cough evolves into coughing spells which can last for three months. Babies younger than four months of age that develop whooping cough do not usually make a whoop sound but typically have severe coughing spells that frequently have vomiting associated with the cough. Some babies even forget to breathe. Babies with these types of symptoms need to be evaluated by a doctor and will likely be admitted to the hospital.

Is it Serious or Not? Guidelines About When to See a Doctor

You should consult your child’s pediatrician if you think your child has a bacterial or viral infection other than the common cold, which is not usually serious.

Sometimes it will not be clear whether your child has a viral or bacterial infection because many ailments can be caused by either type of microbe. This means the doctor will need to physically examine your child and ask you questions about their medical history. If needed, the doctor may ask for a blood, urine, culture test, or biopsy of body tissue, to confirm a diagnosis.

You should bring your child to a doctor if you see any of the following signs develop:

  • Dehydration: Your child may be dehydrated if he or she is drinking less than normal, urinates less than three times in a 24 hour period, or is crying without producing many tears.
  • Breathing difficulties: Your child may have trouble breathing if you see him or her taking faster breaths, having flared nostrils, or visibly using their ribs, stomach, or neck muscles to breathe.
  • Reduced activity: As their parent, you know your child’s normal level of activity and responsiveness more than a doctor or anyone else. If this is markedly reduced, it’s time to take your child to the doctor.
  • Elongated symptoms: If your child is experiencing symptoms or isn’t feeling well with no improvement in three to five days.
  • Fever: If your child is younger than three months old and has a fever.

How K Health Can Help

Get Answers, Fast.

Did you know you can get affordable primary care with the K Health app?

Download K Health to check your symptoms, explore conditions and treatments, and if needed text with a clinician in minutes. K Health’s AI-powered app is based on 20 years of clinical data.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Howard Jeffries, MD

A pediatric cardiac intensivist at Seattle Children's Hospital, Dr. Jeffries is also Senior Medical Director, Regional Network. He completed a residency in pediatrics and a fellowship in pediatric intensive care. He has published chapters and peer-reviewed articles, with an emphasis on cardiac intensive care, informatics, outcomes assessment and quality improvement.