In the post titled “A deeply shocking scene from the local swimming pool”, the relative accused the day care worker of child abuse and violently shoving the boy – despite not witnessing the incident.

Comments flooded in and the post was circulating across other mom cafes. Before long, users had identified the employee and began sending her angry and threatening messages.

Two days later, the woman – whose identity has not been released – took her own life.

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The case drew more public attention to online groups that have been the subject of a complicated debate in recent months, as their members have been accused of using their clout in harmful or dishonest ways.

While being a space where mothers can seek insight and support, the groups also confer a sense of strength in numbers and members have mobilised in the past against businesses or educational institutes they accuse of unsafe or unclean practices. In an infamous case, three members of a mom cafe reportedly posted unfounded criticism of a food outlet in Seoul after the owner refused to give them free food.

In another case, a driver who worked for a taekwondo institute in the capital was accused of operating a bus unsafely when driving children home after a lesson. The online criticism led to the institute’s closure.

South Korea has one of the world’s lowest birth rates, in part because of the high cost of raising and educating children.

“In Korea, motherhood has become a kind of privilege, something that requires a middle class or above lifestyle,” said Alex Taek-Gwang Lee, a professor at the Kyung Hee University School of Global Communication. “Some mums therefore consider themselves people who have status and power over others.”

Nevertheless, most activity on mom cafes is benign, consisting of tips and recommendations. Yoon Ji-young, a 34-year-old office worker who gave birth to her first child earlier this year, is a member of South Korea’s largest mom cafe – Moms-Holic.

She said she found the forums to be a useful source of quality information.

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“Books have really typical or standard ideas, but babies’ situations can vary a lot, so I refer to advice from the cafe because it’s more practical and based on experience,” she said. “We cheer each other up. We always say that you are not the only one who is suffering when a baby is in a bad situation.”

As mothers are active consumers of the wide array of products marketed to parents of small children, Mom cafes also present a commercial opportunity. Many of the groups have rules to keep out members who are not really mums, such as salespeople seeking to promote products or services.

They also have gatekeepers who try to guard the groups from greedy or unscrupulous outsiders, and anyone who wants to become a member has to jump through a series of hoops before being permitted to fully participate in the online conversation. To be accepted as a member of Moms-Holic, Yoon had to first prove she was not a bot or scammer pushing a fraudulent business, and was willing to spend time taking part in the group’s discussions.

Before being granted full membership, new users have to upload about 10 articles to the message board – or 30 replies to ongoing discussions – that moderators have deem appropriate.

However, the groups do not have mechanisms to prevent members from mobilising in an attempt to shame a business or person. After recent controversial incidents, some have called on the government to police the groups’ content, but authorities haven’t taken any action yet.

“By forming public opinion as a community, mums can act collectively to solve social problems. But too often mums think only of themselves and their child, and they act selfishly,” said Lee Sung-eun, a 28-year-old who gave birth to her first child earlier this year.

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South Korea provides subsidised child care for children younger than six, but has not been able to ensure high-quality care across the board. This has led to a lack of trust in services provided by the state, said Sung-Hee Lee, a lecturer in sociology and social policy at the University of Derby in Britain.

“[A] lack of trust in childcare provision in South Korea has brought more informal reliance, such as relying on in-laws or aunties and so on,” she said.

Lee Yeon-hee, a 33-year-old with a one-year-old daughter, is a member of the biggest mom cafe in the city where she lives and feels mums need to exercise caution with any information they find online.

“A lot of mums rely on information from the cafes, then sometimes fully absorb it,” she said. “Rather than uncritically trusting the information we find on mom cafes, much of which is posted anonymously, we need to keep in mind the effect such actions can have and act responsibly.”