Night-time technology use is disrupting the sleeping habits of children and damaging their mental health, the effects of which are becoming increasingly apparent in classrooms, educators say.

The trend is causing some children to behave like device vampires, according to teachers in Canberra, who report students whose sleep cycles are pushed out as they play on phones and tablets into the early hours of the morning, then sleep through the school day.

"Ten or 15 years ago, this was not an issue at all," Liz Bobos, co-president of ACT Principals Association, said.

"We tuck our children into bed, we read them a story, we say goodnight and we assume that eyes are shut — but there's no guarantee that that happens."

School staff say and the services available to children presenting with mental health issues are limited.

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Ms Bobos said schools have seen an increase in referrals to psychologists, but that many youth mental health programs run by groups like Headspace did not begin until the age of 12.

Latham Primary school teacher Erin Weston said some of her students have confided in her that they are self-harming, but getting access to health services can be difficult.

"Even primary kids are self-harming … they tell me it's a way to help cope with the stress and anxiety," she said.

"I've had a lot of students over the years who have had anxiety or other mental health disorders, [but] it's hard to get access to support for them when they're in the primary schools years. It tends to be 12 and up or 13 and older."

Professor Sarah Blunden, director of the Australian Centre for Education in Sleep, explains that the blue light in mobile devices delays the release of melatonin, pushing back the body's circadian rhythms — the cycles which determine when we sleep and wake.

"And because our circadian clock does have a distance to run, because we go to sleep later, we are alert later," Professor Blunden said.

Broken body clocks create 'teary and moody' students

Professor Blunden said disrupting your body clock affects hormones, appetite, metabolism and mood.

"If you have a disrupted circadian clock, one that is delayed, but also one that is different day to day," she said.

"You are more likely to have an emotional lability, that is, a much more volatile emotional state. You're more likely to be depressed or have waves of depression or anxiety."

Ms Weston said she has seen that disruption in the classroom.

"We've had students in the past who struggle with their emotional regulation much more; their highs are higher and the lows are much lower," she said.

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"They can be really teary and quite moody."

Ms Weston said parents often did not know their kids were missing sleep.

"Sometimes [we make] a phone call home to say 'Are you aware your child [was] on the device last night?' and sometimes the parents don't know. Sometimes teachers are the first port of call to let them know," she said.

Ms Bobos said schools and parents needed to work together to make sure kids were using technology appropriately.

"It's a joint effort I suppose between schools and parents. Schools have a huge role to play in teaching children … about creating balance in their life," she said.

"There are apps that parents can put on their own phone that don't restrict children from accessing technology, but allow parents to know what apps their children are accessing, so parents can have a conversation with their kids. There's a real opportunity for parents to educate children there."