They are incubators of disease, harbouring dirt and bacteria. They spread germs wherever they go. And they are in the classroom every day. Learning.

Eighty-four per cent of children do not know how to avoid spreading germs when they cough or sneeze, according to a new study conducted by the Department of Health. It reveals that more than half of children are taught to sneeze or cough into their hands, rather than into a tissue, and only 10 per cent wash their hands immediately after coughing or sneezing, the practice recommended by medics.

A fifth of 1,000 mothers surveyed admitted that they do not know the best way to tackle coughs and colds, or to stop them from spreading.

Chris Davis, of the National Primary Headteachers’ Association, is not surprised.

“Secondary teachers are always telling early years teachers they couldn’t cope with the runny noses and snotty kids,” he said. “It happens, of course it does. As do wet pants, grazed knees, the lot.

“But we’ve probably taken hygiene measures too far. A lot of people fear we’re actually spoiling children’s immune systems by not allowing them to play in the mud.”

To educate early years pupils about the dangers of incubating germs on their hands and sleeves, the Department of Health has produced a picture book.

Dirty Bertie depicts a character who sneezes over everyone, shows his used tissues to his friend, and reaches for cakes without washing his hands after using a dirty tissue.

Just like Bertie, children are encouraged to throw away used tissues carefully and to wash their hands as soon as possible after coughing or sneezing.

Mr Davis doubts the practicality of continual hand-washing. “Obsessive compulsive cleanliness would be a worry,” he said. “There’s certainly been a growth of that sort of attitude.”

But Katherine Ashenburg, author of Clean: An Unsanitised History of Washing, points out that a third of adults fail to use soap in cinema or restaurant toilets. Schools, therefore, may be better placed than parents to give lessons in hygiene.

“Teaching children how to wash seems to be one of those things we decide to do every 30 years or so,” she said. “We’ve always got a new crop of children. Or it doesn’t ever catch on. Or standards of cleanliness change.”

In Toronto, a campaign is exhorting public transport users to sneeze into their elbows, rather than hands. “I’m sure some primary teachers have talked about that in schools,” Ms Ashenburg said.

“And in Japan they’ve long been obsessed with people with colds wearing hospital masks, so they don’t spread germs to anyone.

“So who knows what’s next?”