News a baby boy is among New Zealand's latest Covid-19 cases has further dispelled the myth children can't catch the virus at a time when parents contemplate a potential return to school for some youngsters.

Three boys aged under 1-year-old have now caught the virus in New Zealand, including two infants in the country's far south and one in the Waikato.

The Southern DHB wouldn't comment on how the two babies in its region are faring, while Waikato DHB only confirmed it had no babies in hospital with coronavirus.

Normally virus outbreaks hit the very young and the very old hardest.

Yet internationally, children seemed to be suffering far fewer severe coronavirus infections than the elderly in what had been a relief to parents the world over, former president of the Paediatric Society Dr Nick Baker said.

Just 34 children under 9 had so far been diagnosed with Covid-19 compared to 342 cases among 20-29 year olds and 110 cases in over 70-year-olds.

"However, some children will still get very sick," Baker said.

"And it is certainly not a condition that you want your kids to get by any means."

Overseas some children have died from the virus and for those who do become unwell, Covid-19 can be a terrifying condition in which a patient often suffers alone, away from loved ones.

Infants most at risk of a severe infection were those with an underlying condition that already made it harder to breathe or cough, Baker said.

"So if you have cerebral palsy or muscular dystrophy or Down Syndrome, something that means your cough is not as strong or has other weaknesses, it is going to be worse," he said.

"And similarly for children whose immune systems may not be as strong, they may have more illness."

"But there also seems to be the random bad case - absolutely no reason why this person does terribly with this germ."

Infants could be tested for Covid-19 in the same way as others, by collecting a sample of their "snot" from their nose or mouth.

"It is not pleasant, but kids tolerate it well," Baker said.

Further muddying the waters about children and the coronavirus outbreak is their potential role as spreaders.

"For so many viruses children are often a spreader because of the nature of the fact they are less careful with their secretions and coughing and sneezing," Baker said.

That could become an increased risk now the Government was set to decide tomorrow at 4pm whether the nation would leave its hardline alert level 4 lockdown and enter a slightly eased alert level 3.

Under alert level 3, children could return to school if no one was available to care for them at home.

"So the plan would be to try and keep the bubbles small at school, but, as you know, preschoolers will just mix," Baker said.

"So I think that is the reason why there are a lot of concerns from the education sector and early childhood sector about how realistic this is going to be."

Then there was the potential for children to be asymptomatic carriers of Covid-19, taking it into the formerly safe bubbles of elderly relatives.

Baker pointed to recent results from the US aircraft carrier the US Theodore Roosevelt, indicating the strength of the global outbreak may be partly due the number of asymptomatic carriers.

• Covid19.govt.nz: The Government's official Covid-19 advisory website

The navy said about 60 per cent of the more than 600 sailors from the vessel who tested positive for the virus had yet to show symptoms of it.

"This is the challenge for the Government this week," Baker said.

Currently, New Zealand appeared to have very little free flow of Covid-19 around the community, he said.

"But are the risks low enough to let people start mixing or is there a risk we will get this asymptomatic spread and - as we've seen with some of the New Zealand clusters - a single person can infect a very large number of others?"

"It is a tough position but also a very lucky position to be in to make this choice."

Eradicating Covid-19 was a bold ambition, he said.

"It is yet to be known whether that is possible or whether it will just grumble on a bit like we see with whooping cough or what used to happen with polio," he said.

"It lingers in the community and then it flares up with devastating consequences, then it dies down, then it comes up again."

"We will have to see what happens."