Chickenpox has been shown to have fatal complications
The Roberts were taking their family of four children away for a weekend when their two-year-old twins started to show the first signs of chickenpox.
Their mother Helen, a GP from Farnham in Surrey, admits she was at first unfazed by Will and Peter's spots, as she knew there had been an outbreak of chickenpox at their nursery.
For the first two days they appeared reasonably well, but then Will seemed to go rapidly down-hill.
He developed a fever and started to vomit.
"The next morning he vomited once and although clinically there was still no reason for concern, my maternal gut feeling was telling me otherwise, so I took him to casualty," Dr Roberts said.
"The receptionist didn't share my concern and we were shown to a waiting area where I began to question my judgement in the full knowledge that being a mother and a doctor is never easy when trying to rationally assess your child."
Dr Roberts said she had wanted Will to have anti-virals, but was unable to articulate why.
Within a very short space of time Will's condition deteriorated, his heart stopped and, despite desperate attempts to resuscitate him, he died.
At about the same time his twin Peter was admitted to hospital suffering from fits.
Having watched the devastating effect on her own young and previously fit family, and after hearing about other similar tragedies, Dr Roberts became committed to campaigning for a national screening programme.
Chickenpox was not mentioned at all on Will's death certificate and Dr Roberts fears this is the case in many similar deaths, leading to a serious under-reporting of adverse incidents.
'Tip of the iceberg'
"Just hearing from my colleagues I realise that what they know about it is the tip of the iceberg.
"I think it is definitely being under-reported. Generally people do not like to bother their doctor about chickenpox because they think it is mild.
"But I think there needs to be more awareness."
She blames a growing lack of natural immunity for the disease becoming more virulent.
This could be partly blamed on the fact that most children are now vaccinated against virtually every other childhood disease, she says.
"I think our immune systems are not as good as they should be because we are vaccinated against all the other elements.
"At the moment most people in the medical profession think chickenpox is not bad for you."
Dr Roberts admits that until Will's death she had not realised just how serious the disease could be.
"I personally would not have worried unless the patient was immunosupressant or pregnant. I would not have worried about a child unless it was a very young baby.
"Now I tend to treat it more aggressively."
'No vaccination plans'
In the US, chickenpox is vaccinated against, and a vaccination programme is also being started in Israel.
But a spokesman for the Department of Health said there were no plans to start vaccinations in the UK.
"There is no evidence that chicken pox has become a more serious infection or that that the population's immune systems have become less able to deal with chickenpox.
"At present chickenpox (varicella) vaccine is not licensed in the UK. Its use is, however, recommended in immunocompromised individuals, particularly children with leukaemia or solid organ transplants."