Three weeks of what he had gone through was exceptional

Bevis Jones, father

Her condition is described as stable.

Pneumonia caused by chicken pox is extremely rare and occurs when the disease affects every organ in the body.

The children�s' mother, Suzanne Jones, said: "We are hoping they can provide an answer and kill the virus in Rebecca.

"Then we will get our little girl home."

Aaron's life support machine was switched off on Monday after his parents were told nothing more could be done for him.

Chicken pox is unpleasant but rarely fatal

Mr and Mrs Jones, from Abbeyfields in Wigan, believe their children developed the virus because of hereditary weaknesses in their immune systems.

Aaron was treated at the high dependency unit of Pendlebury Children's Hospital in Salford and then at Booth Hall Children's Hospital in Manchester.

Mrs Jones said: "It was a very, very rare case ... the people at Booth Hall and Pendlebury had not seen the likes of it before."

Aaron's father Bevis added: "The doctor explained to us how much of a fighter Aaron was and three weeks of what he had gone through was exceptional.

'Fought to the end'

"An adult is only expected to last one week, so he fought through to the end."

Aaron twice contracted meningitis when he was younger, leaving him with hearing difficulties. This could have weakened his immune system.

Serious complications are very rare and I would not want parents to be frightened

Dr Robert Aston

A consultant in communicable disease control for Wigan and Bolton Health Authority assured parents that complications as a result of chicken pox were uncommon.

Dr Robert Aston said: "Serious complications are very rare and I would not want parents to be frightened.

"Measles is actually much more dangerous, and parents can protect their children against that by the very safe MMR vaccine."

Chicken pox is a viral infection that causes a blister-like rash on the surface of the skin.

It usually appears first on the trunk and face, but can spread to the scalp and inside the mouth, nose and ears.