A warning over increasing outbreaks of flu across Horsham, Crawley and Mid Sussex has gone out from NHS bosses.
Now Sussex Clinical Commissioning Groups - which pays for healthcare across the region - is urging parents to get children vaccinated.
They say that there was a steady rise in flu cases last winter.
A spokesman said: “Flu can be a very unpleasant illness in children causing fever, stuffy nose, dry cough, sore throat, aching muscles and joints and extreme tiredness, which can often last several days and requires parents and carers to take time off work to care for them.
“Some children can get a very high fever, sometimes without the usual flu symptoms, and may need to go to hospital for treatment.
“Serious complications of flu include a painful ear infection, acute bronchitis and pneumonia.”
Crawley Clinical Commissioning Group chairman Dr Laura Hill said: “We’re urging parents to take up the offer of vaccination for their children as it’s the best defence we have against this unpredictable virus.
“It is important we protect young children from the flu and we know children tend to be ‘super-spreaders’ of flu, so protecting them is crucial for protecting the rest of the family.
“The nasal spray is safe and tailored each year to specific flu viruses – so please claim this free NHS offer.”