At one Australian school, Year 8 girls are setting each other self-harm challenges.

Warning: This article contains information about suicide and self harm which may be distressing for some readers.

Self-harm is now so common among Aussie kids that at one school, young girls had formed a self-harm club.

Former teacher Rachel Downie found out about it through her website, Stymie, where children can make anonymous reports of harmful behaviour.

"Not long ago a high school contacted me and said that they had found out that there were girls in Year 8 who actually had self-harming challenges, like a club," Downie tells Mamamia.

"A couple of schools have told us that [self-harm] is happening in primary schools."

The website receives an anonymous report from a child, on average, every four minutes. Often, a screenshot is attached as proof. A notification is then sent directly to that child's school. More than 100 schools around Australia have signed up to the service.

As well as self-harm, Downie says kids are reporting other children bullying and cyberbullying each other, bringing drugs and weapons to school, and talking about suicide.

LISTEN: Bec Sparrow talks to Holly, Mia and Jessie on Mamamia Out Loud about the dangers of cyber bullying and what we can do to stop it... Post continues after audio.

"It's become part of our kids' vernacular to talk about killing themselves as a way to cope," she says.

"These sorts of things come from nobody monitoring these conversations. Kids make posts on their Streaks or their Snapchats talking about wanting to die. That happens on a daily basis. And unfortunately we end up with cases where kids do die."

Even if children aren't talking about suicide themselves, it can be very upsetting for them to see their friends talking about it.

"They actually bear the weight of some of this stress," Downie says.

Often, kids won't report harmful behaviour to teachers at school because they don't want to lose their friends over it. Most of the time, they won't tell their parents about it either.

"We're beyond the point where we can say, 'Look, my kid is a really good kid. They would tell me.' We know that in a lot of cases they don't."

So why won't kids tell their parents about upsetting things that are happening online?

There's one big reason: they're afraid their parents will take away their devices.

"We are seeing a lot of addiction behaviour in kids and they do want to keep their devices and stay connected," Downie says.

She says there are "alarming" numbers of primary school kids using anonymous messaging apps that are only supposed to be used by 13 years and up. She firmly believes that parents should be vetting their kids' conversations on social media through primary school and into high school.

"I don't know any nine-, 10- or 11-year-old who has the capacity to measure their words. They don't have those forward planning skills. They certainly don't have the emotional intelligence," she said.

Downie believes parents need to teach their kids how to have conversations online.

"I spent three months teaching my daughter how to ride a bike, and the worst thing that was going to happen was that she'd skin her elbow or her knee. Have you spent three months teaching your kids digital values?" she sayd.

"Don't say something online that you wouldn't say to someone's face. Don't post photos of people without their permission. Make sure you're upholding our family values when you're in those places as well."

LISTEN: Robin Bailey and Bec Sparrow discuss the complexity of teens, social media, and the firecrackers that we see when the two mix.

She says parents need to step in and supervise, even if they've already given their 11-year-old a phone and let them do what they want on it.

"It's not about banning them all together," she explains.

"It's about having an appropriate presence. There are some great apps out there to help parents actively supervise and then move more into passive supervision as their child grows.

"As adults, we need to take some of our control back."

If you or someone you know needs help you can call Lifeline on 131 114 or Beyondblue 1300 224 636.