The condition is known as RSV illness (Respiratory Syncytial Virus) and can cause severe breathing difficulties for some young children.
It is one of the many viruses that cause coughs and colds in winter, but staff at Royal Preston Hospital say they have seen a lot of cases in recent weeks, months before the usual time for colds and flu.
They say this could be because the virus, which, like coronavirus or flu, is highly infectious has only just had chance to start spreading as people have been mixing more this summer after the end of Covid lockdown restriction.
And, while RSV normally lasts for just a few days and clears up by itself with a bit of help from paracetamol and ibuprofen and plenty of fluids, in under twos, it can lead to a more severe infection and bronchiolitis - the inflamation of the smaller airways in the lungs, plus the production of mucus - resulting in a range of potentially dangerous breathing problems.
Because many under twos have not been exposed to colds as much due to the previous lockdowns, Public Health England has been preparing for a higher than normal number of cases with potentially 50 per cent more hospital admissions than normal.
Dr Sathiyapriya Kandasamy, clinical director from the paediatric ward at Royal Preston Hospital, said the paediatric wards have been full over the past few weeks, mainly due to the significant rise in infections.
She said: "It is a common infection in children which we normally see in winter months, but the cases have significantly gone up which ins very unusual for this time of year. We think that's because for the past one and a half years of lockdown children have not been mixing with each other until now.
"Compared to the whole of England, the North West has seen a significant surge, the highest in the country.
"Normally it is a self-limiting condition and after the first three days children get better. But premature babies or those with other conditions, or some young children can become very unwell with it."
She said parents should be looking out for warning signs such as infants getting cold-like symptoms which continue to get worse after three days, with difficulty breathing, grunting when breathing, being unable to feed due to poor breathing, high temperature and a general floppiness of behaviour.
She said parents should contact their GP or dial 111 but if the breathing worsens or there are long pauses in breathing or if the child's lips become blue, then the child should go to hospital.
She added that the precautions taken to avoid the spread of coronavirus - the proper washing of hands, keeping infants away from others with colds or flu, keeping them at home when they have a cold, will help prevent spread of the RSV infection.