The UK government says schools in England could start to welcome some year groups back from 1 June, as long as five “key tests” have been met.

Perhaps the only corner of comfort to be found so far in the covid-19 crisis is that children appear to be less vulnerable to serious complications from the virus.

Nevertheless, a letter from a Kent headteacher telling families he would “rather any child repeats a year than go back too soon and have to lose a child” has been shared widely on social media.

Understandably, parents are worried about the risks kids might face once they return to class.

Let’s take a look at what we know.

How many children have died with coronavirus?

Since the outbreak began, two children aged under 15 have died after testing positive for coronavirus in England and Wales.

These are, of course, tragedies for the children and families involved. But if we’re thinking about the risks posed overall to children, it is important to consider them in context.

Professor Sir David Spiegelhalter at the University of Cambridge estimates that the risk to children of catching and then dying from coronavirus is one in 5.3 million.

(That’s based on two deaths out of a population of 10.7 million under-15s in England and Wales.)

It means that on average, under-15s face the lowest coronavirus fatality risk of any age group. The over-90s face the highest risk, with a one in 81 chance of catching and dying from the disease, according to Professor Spiegelhalter’s calculations.

What about this new inflammatory syndrome?

In recent days, more reports have emerged about what seems to be a new inflammatory syndrome that doctors in Europe and the US have started to report in children since the coronavirus outbreak began.

As FactCheck reported last month, the condition was the subject of an alert sent out to clinicians in England in late April.

It’s now believed up to 100 children in the UK have been treated for the condition, with a small number needing intensive treatment.

This is clearly concerning for the families involved – but experts say the syndrome is “exceptionally rare”.

100 cases out of 12.7 million children in the UK suggests the chance of a child developing the inflammatory syndrome is, on average, around one in 127,000.

In an interview with Channel 4 News last night, Dr Liz Whittaker of the Royal College of Paediatrics and Child Health said there is “a spectrum” of severity among patients with the inflammatory syndrome.

“Unfortunately some of the children have been extremely unwell and have required intensive care support”.

Though she said that out of three children who had needed ECMO – a treatment for extremely ill patients – two “have done very well, despite being the most severely unwell” of those with the syndrome.

Dr Whittaker said “the majority [of children with the syndrome] get better within four to six days, and we have a cohort of them who are already at home with their parents and being closely monitored”.

“We would encourage any parent who’s worried about their child to take them to either their GP or to A&E if they’re worried, because it’s more likely they’re unwell with another condition rather than this inflammatory condition”, she said.

Indeed, it’s not yet certain that the new syndrome is caused by the coronavirus, as not all those presenting with symptoms tested positive for the virus. Scientists are therefore “being cautious and we’re saying that it’s associated with the pandemic while we get more information”, Dr Whittaker says.

But in the meantime, it’s “reasonable to assume” that the two “might be related”.

How does the coronavirus compare with other risks children face?

The winter of 2017-18 saw an unusually aggressive outbreak of flu take hold in the UK and other countries.

Over 50,000 excess deaths were reported here, according to the Office for National Statistics – slightly more than the equivalent figure for the coronavirus outbreak so far.

Of those who died in the flu season of 2017-18, there were 16 “influenza-related deaths” among children aged under 18, according to government data for England.

Using the same methods as Professor Spiegelhalter, we might therefore estimate that the fatality risk children faced from the 2017-18 flu outbreak was around one in 742,000.

(That’s based on 16 deaths out of 11.9 million under-18s in England in 2017).

On this basis, we tentatively estimate the mortality risk to children from the 2017-18 flu outbreak was around seven times greater than the risk they currently face from coronavirus.

Now, there are important caveats to bear in mind here.

Coronavirus appears to be much more contagious than flu. And unlike flu, it has prompted near-total lockdown of societies across the world. The threat of covid-19 right now might be lower than flu for children precisely because we’ve taken more robust steps to control it.

So where does that leave schools?

Asked about the factors policymakers should consider when reopening schools, Professor Russell Viner of the Great Ormond Street Institute of Child Health said yesterday: “Well how do we balance risks in normal life? The total numbers of children who get this [new inflammatory] syndrome are very small.”

He considers how we mitigate the risk of other causes of death in children: “160-170 die in car crashes [each year]. Those deaths are tragic but also rare. How do we manage those? We take steps to prevent these deaths. We buy child seats, we use seat belts, we sometimes buy better cars. But we don’t stop driving.”

“This [inflammatory, coronavirus-associated] syndrome is much, much more rare than car accidents involving children. So it should not stop parents sending their children back to school when schools are ready to re-open” Professor Viner said.

And he points out that “we all know that there are many harms for children of lockdown as well.”

What’s happened in countries where schools have reopened?

Schools in Israel were told to allow pupils back from 3 May – though uptake has been patchy, with just 60 per cent of eligible pupils returning to class, and individual cities deciding to stay shut.

Dr Hagai Levine, an epidemiologist at the Hebrew University of Jerusalem and the head of the Israel Association of Public Health Physicians, told the Times of Israel that based on what we know about covid-19 “the balance is very clear in favour of opening”.

As for why so few students have returned, Dr Levine speculates: “Unfortunately, in Israel, the decision on opening of the schools was not handled very well”, which led, he said, to a “confused” system.

In schools that have opened there, class sizes are capped at 15, with children aged 7 and over required to wear face masks.

In Denmark, some primary school children were allowed to return from 14 April. Pupils are segregated into groups of no more than 12 throughout the day and can’t mix with others. Hygiene also plays a significant role: “there is pretty much hourly hand-washing going on”, says one Danish teacher.

The leader of the Danish Union of Teachers says “We are glad to say the re-opening up to now has been quite successful” – though some parents remain concerned.

Given the time it takes for coronavirus infections to develop into symptoms – and the fact that the rare inflammatory syndrome associated with it may take even longer to manifest – we don’t yet know if there have been more infections among children as a result of schools reopening. We will have to wait for data to arrive.

What about children passing the virus to others?

The decision to open up schools is not just a matter of working out the risk to children. We also have to consider the risks to staff who look after them, and whether – even if they don’t develop symptoms – kids might help transmit the virus between households.

Education unions in the UK published a joint statement this week saying “it appears, school staff will not be protected by social distancing rules” and calling on the government to “step back from the 1 June [potential reopening date for England] and work with us to create the conditions for a safe return to schools”.

Like many things linked to coronavirus, the science is not yet settled on children’s capacity to pass it on.

A recent study from Germany of nearly 4,000 covid-19 patients concluded “children may be as infectious as adults”. Based on these results, the authors wrote: “we have to caution against an unlimited re-opening of schools and kindergartens in the present situation”.

But the UK government’s chief pandemic modeller, Professor Graham Medley, said this week that the “current understanding” is that children are “not playing a key role” in transmitting the disease.

And in Denmark, the “R0” value – how many people someone with the virus goes on to infect – has actually fallen since schools partially reopened. England’s Education Secretary, Gavin Williamson, told MPs: “schools have started to return in Denmark and have not seen a negative impact as a result of that. This has reconfirmed this approach is the right approach.”