The move comes after a 58-year-old man tested positive for the virus, with no clear links as of yet to a managed isolation facility.
The man, who was not yet vaccinated, lives in the Auckland suburb of Devonport. He visited Coromandel township while possibly infectious, health officials said.
Ardern acknowledged that in the past, special arrangements have been made for children of essential workers such as police officers, those in healthcare and supermarket workers.
"That is not something we will be able to stand up in three days," Ardern said, adding that there may be other arrangements made if the nation stays in level 4 lockdown beyond that.
Frustrations were high among parents during previous lockdowns, even with the lesser restrictions.
"I'm a good mum but a useless teacher, my son also hates being home, he loves school," one mother told the Herald in February.
Even with children of essential workers allowed to attend school at the time, the Auckland Primary Principals Association reported a massive drop in attendance during the February lockdown.
Some of Auckland's biggest secondary schools, with normal attendance of 2000 to 3000 students, reported less than 10 students showing up on the first day of that lockdown.
Ardern today acknowledged the difficulty for both parents and teachers in the days to come.
"They have done this before. I know how hard this is," she said. "I understand what we are asking of them."
One thing that will be allowed again for harried parents and cooped up children are neighbourhood walks. Ardern said it is fine for families to go for a stroll or ride a scooter through their neighbourhoods when they need a break from home learning, but the exercise comes with caveats.
"We ask people to stay two metres away from anyone you pass," she said. "Stay local. Do not congregate. Don't talk to your neighbours. Please, keep to your bubble.
"We know from overseas cases of the Delta variant that it can be spread by people simply walking past one another, so keep those movements outside to a bare minimum, wear a mask and make sure you keep up that physical distancing."
Auckland Primary Principals' Association president Stephen Lethbridge said this evening schools in the region are very well prepared for the transition back to home learning.
"We've learned a lot from each subsequent lockdown, and each time we do it a little better," he said.
That being said, it's going to be difficult for everyone, parents included, adjusting to level 4, he added.
"There will be some teachers and principals working very late into the evening," he said.
Many schools around the country spent the afternoon preparing for the possibility of lockdown, even before it was made official this evening, Lethbridge said. He predicted most will contact students and their families either this evening or tomorrow morning as plans get solidified.
Just this morning, before a community Covid case was announced, schools across the country were reminded to be ready for things to change at short notice. Secretary of Education Iona Holsted said although "we're all still enjoying alert level 1 across the country", it was concerning to see the Delta variant sweeping the globe.
Schools should check they were ready if things change, particularly if they were linked to a confirmed case, Holsted wrote.
In an updated bulletin to schools this evening, Holsted directed schools to take an especially conservative approach to the virus as the lockdown kicks in.
"I realise that children may have headed home without their devices," she wrote. "Because of the importance of the first 24 hours in tracing this virus, at this stage there is no exemption process to allow for devices or hard pack resources, or any other approved arrangement. We will continue to review this and if this changes we will let you know."
School hostels and residential special schools should also send students home during alert level 4, the Ministry of Education said in this evening's updated guidance to schools.
However, an exception will be made for students who cannot safely return home, such as international students.
