Almost a quarter of the children’s beds at NGH are being taken up with young flu patients.
It has forced doctors to limit visits to parents and carers only, to stop the spread of the virus among already weak children.
A hospital spokeswoman said the measures were likely to stay in place for several weeks until the current outbreak had passed.
She said: “The measure is to reduce the risk of the other children on the wards, some of whom are very vulnerable to infection, picking up the virus.
“It’s in response to an increase in admissions of children with flu.”
Early this week, seven children were being treated for confirmed flu, a fifth of the overall capacity on the paediatric wards, with a further three admitted with flu-like symptoms.
The limits on children’s wards are on top of the general warning already issued by NGH for anyone planning to visit the hospital to stay away if they or their family members have flu or flu-like symptoms.
The spokeswoman said: “By visiting while ill, visitors can easily bring the virus into hospital.
“This can be particularly serious for people who are already frail and ill or who have a suppressed immune system due to a long-term condition.”