RSV infects most babies by the age of two
Parents are being warned to be on the look out for a potentially-fatal winter baby infection.
The British Lung Foundation said October heralds the start of what is known as the RSV season.
RSV - respiratory syncytial virus - affects most children by the age of two. For most it causes no more than a cold, but can be serious for some.
A survey of 500 parents found nine out of 10 were unaware of the symptoms and dangers.
Chest infections due to RSV are the most common cause of hospital admissions for young children, with about 20,000 under ones being admitted each year.
But the poll showed only one in 10 parents were aware of this with half believing meningitis was the biggest risk.
In the most serious RSV cases, children can develop bronchitis or pneumonia and - albeit very rarely - die.
Babies born prematurely or those with heart defects are particularly at risk.
Professor Warren Lenney, of the British Lung Foundation, said: "RSV affects nearly all children at some point in their early years so parents need to be aware of the symptoms and to know when they should seek medical attention."
Symptoms of the condition usually first appear in the form of the common cold.
These include runny nose, mild fever, sore throat, mild cough, blocked nose and ear infection.
After three to five days symptoms may worsen as the virus spreads to the lungs, causing breathlessness, rapid breathing, wheezing and a strong cough.