Parents are being urged to vaccinate their toddlers against flu to protect them and others from severe illness this winter.
Chief Medical Officer Dame Sally Davies described children as "superspreaders" warning they could easily give the virus to a large number of people including relatives.
She said: "Flu can be really nasty for toddlers, leading to time off nursery which has a big impact on mums and dads and sometimes even a stay in hospital.
"They also spread the virus easily and often pass flu to grandparents and other relatives who can become very ill, fast.
"Giving two, three and four-year-olds the free nasal spray really is in everyone's interests if you want to help avoid a miserable winter for all the family."
Children are eligible for a free nasal spray flu vaccine from their GP but only one in four have received it so far.
Flu can cause a fever, sore throat, aching muscles, extreme tiredness and even complications such as bronchitis and pneumonia if caught by a child.
Youngsters are more likely to spread the virus because they tend to have greater contact with others and may not cover their mouths when coughing and sneezing, or wash their hands enough.
Pregnant women, under-65s with long-term illnesses and over-65s are also eligible for the free spray on the NHS.