Doctor's Notes on Flu in Children (Childhood Influenza)
Flu in children (childhood influenza) is an acute viral infection of the airway and occasionally the lungs, caused by types A, B and C with type A serotypes causing the most severe disease. Signs and symptoms start about 2-4 days after exposure to the virus and include fevers (up to 104 F), chills, muscle aches, abdominal pain, vomiting and diarrhea and in infants less than 6 months may show lethargy, poor feeding and poor circulation. In most children, the symptoms last about 3-4 days and resolve but the cough and tiredness may last longer (1-2 weeks). If symptoms become severe, the child needs to be seen by a pediatric caregiver.
The cause of flu in children are influenza viruses. Many children recover spontaneously; however, some viral serotypes like H1N1 may cause severe disease in more children than other serotypes. The CDC recommends that EVERYONE 6 months of age and older get the yearly flu vaccine.
Cold & Flu : Influenza vs. Common Cold Quiz

Which illness is known as a viral upper respiratory tract infection?
See AnswerREFERENCE:
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.