The Health Department says it is worried that parents are underestimating how serious influenza can be on children.

The department has revealed that less than 20 per cent of Western Australian children have been vaccinated for this year's flu season.

It has also released new research revealing how quickly influenza took its toll on 15 children who were admitted to intensive care last year.

Of those, 4 children died from complications associated with the flu.

Dr Paul Van Buynder says children should be receiving the first of two flu vaccinations now.

"Somewhere between 2 and 5 per cent of all children are admitted to hospital because of influenza related complications," he said.

"We think it's very important that parents understand that this a very serious illness for children."