Children should be vaccinated before Christmas to avoid putting older relatives at risk of infection, warned the chiefs of the NHS.
Doctors say the virus can spread more easily in schools and daycare centers, putting grandparents and others at risk of getting sick during the holiday season.
People with heart or lung diseases and pregnant family members can be especially vulnerable, the NHS warned.
Dr. Paul Cosford said the vaccine was "quick, easy and pain-free."
The childhood flu vaccine is offered annually as a nasal spray to help protect against the flu.
Two and three year old children can get the free vaccine in the NHS, through GP practices.
An expansion of the scheme means that children in the reception clbad and the elementary school years one, two, three and four are also eligible for the vaccine.
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According to the latest figures from the NHS, only 18% of children of school age received nasal spray immunization.
Dr. Cosford, medical director of Public Health England, said the flu causes 8,000 deaths a year in England and Wales.
"The vaccine is the best protection against the flu," he added.
"Last year's nasal spray vaccine reduced the risk of childhood flu by 65%, meaning that it was less likely to spread to family members and others would come into close contact with.
He asked that parents give consent for school-eligible children to receive the vaccine at school.
Professor Keith Willett, medical director of NHS England for intensive care, said the children were "super" scandalous "and the season of flu "traditionally reaches its peak" at Christmas.