COPENHAGEN — The children pressed down on a hand sanitizer dispenser and kept a safe distance from one another as they filed into Ellebjerg School in central Copenhagen on Thursday. But while they settled into their lessons, with a new limit of 10 students per room, some of their classmates remained at home, their families resistant to participating in what they see as a public policy experiment.

Denmark this week became the first country in Europe to reopen schools — nursery and primary up to fifth grade — as a start to lifting a coronavirus lockdown imposed on March 12.

Although the country has reported 6,879 confirmed cases of coronavirus infection and 309 deaths, new infections have been decreasing since a peak on April 1, giving the government confidence that a cautious reopening was possible.

But thousands of families are opposed to sending their kids back to school so quickly.

“For weeks, we have been told by the government how dangerous this pandemic is, and how catastrophic it will be if we don’t practice social distancing. And then, suddenly, we have to send our most precious treasures, our children, out to the uncertainty of the virus outside,” said Jannie Duunkjaer, a 39-year-old mother of three who lives north of Copenhagen.

It’s unclear whether the same opposition will arise in other countries as they try to pivot from more than a month of restrictive measures aimed at slowing the pandemic’s spread. Officials are weighing the negatives of distance learning, which can exacerbate inequality, and the reality that many parents won’t be able to return to work if their children are still home — a point that Denmark’s prime minister specifically noted Wednesday in a surprise visit to a school here.

While a recent peer-reviewed article in the Lancet suggested that school closures are less effective than other interventions in fighting the pandemic, many parents may need more reassurance.

Duunkjaer is part of a Danish Facebook group called “My child shall not be a guinea pig for covid-19,” which has amassed more than 40,000 members.

“How do you guys feel about kids going back to school?” one anxious mother wrote in a group post. “My 10-year-old broke down before sleep. She said ‘Mom, I’m afraid of corona. What if I’m infected at school?’ ”

“Children have a right to protection, and therefore we’re not sending our children to school after Easter — children shouldn’t go to war with an invisible enemy,” a distressed father wrote in another post.

This kind of civil disobedience is rare in Danish society, which is characterized by the high level of citizens’ trust in authorities. But parents like Duunkjaer worry their children are vectors that could lead to the virus spreading further in families and society.

An online protest petition has amassed almost 18,000 signatures. A similar petition has 28,000 signatures in Norway, where schools are set to open at the end of the month.

“I think my youngest daughters in elementary school will be frightened to return to a classroom with all these new strict guidelines, and I don’t believe they will be able to follow the sanitary instructions in that age,” said Duunkjaer, who works in administration.

Yet she will let her fifth-grade son return to school next week because she believes he understands how to follow the precautionary guidelines.

Children not attending classes in Danish primary schools will be registered as “illegally absent.” A high percentage of illegal absence normally leads to a deduction in parents’ welfare benefits, but the Ministry of Education temporarily suspended the statute last week as a gesture to reluctant parents.

The Social Democrats in power here have seen their best poll ratings in three decades because of their response to the crisis. But political commentator Anne Sofie Allarp said that while a majority of Danes support how the government has handled the crisis, the decision to reopen schools is raising understandable concern.

“It is very easy for the government to elaborate a threat to national security and people’s well-being, but it is extremely difficult to defuse the atmosphere of fear afterwards,” Allarp said.

At Ellebjerg School, which is instructing children to wash their hands every two hours while in class, Principal Anne Graah called it “a lovely day, beyond all expectations.” She said about 15 percent of elementary students stayed home because their parents were concerned about sending them back.

“Of course, we were a bit worried when we heard schools are opening up again,” Agnete Bjerring-Bohr said as she dropped her child off there on Thursday morning. “But I do feel we are in safe hands with all these precautions. And our children are not at the same risk as our senior citizens.”

Other families are proceeding more slowly.

“I want to wait for two weeks and see how this goes,” Duunkjaer said. “Many parents expect that the infection curve will explode again in this ‘experiment’, but if it doesn’t, I would be willing to send my girls back to school by then. Better safe than sorry.”