Children with mental health problems were at increased risk of developing a mental disorder as an adult, a new systematic review has found.

The research led by the Murdoch Children's Research Institute (MCRI) and published in Neuroscience and Biobehavioral Reviews, found prevention and early intervention should be targeted at primary school age children and those who are experiencing symptoms rather than waiting for a diagnosis.

The study found experiencing mental health symptoms before 14 years of age and even as young as five were predictive of mental disorders well into adulthood. Importantly, symptoms rather than a diagnosis in childhood were more strongly linked with having a mental health disorder as an adult.

The systematic review of 40 studies assessed the influence of mental health problems in childhood later in adulthood in Australia, US, New Zealand, The Netherlands, UK, Finland, France, Brazil and Spain in over 50,000 participants.

MCRI Dr. Melissa Mulraney said the mental health problems present in childhood were more likely to continue through to adulthood, rather than new disorders being diagnosed.

The study found children with anxiety were up to 10 times more likely to have an anxiety disorder as an adult and those with mood and depressive symptoms were up to 28 times more likely to have depression as an adult. Similarly, children with behavioral difficulties were at high risk of having ADHD or antisocial personality disorder in adulthood.

The review showed having any psychiatric disorder between nine to 16 years increased the odds of multiple psychiatric disorders in young adulthood sixfold. Children who had bulimia at 13 had 20 times the odds of bulimia as an adult.

Dr. Mulraney said most mental health treatment services were targeted at youth or adults despite symptoms largely emerging in childhood.

One in seven Australian children aged 4 to 17 years has a mental health disorder. But of these, only half have accessed mental health services.

Samantha's daughter was diagnosed with severe anxiety, ADHD and autism at age 10.

She said it was a 12-month wait to see a psychologist and occupational and speech therapists and her daughter was still in need of a support worker.

"There is a significant demand for mental health services, which is causing long wait times and delaying treatment," she said. "My daughter would be in a very different place now if she had received medical intervention earlier."

Samantha said it was essential that teachers were better trained to identity mental health problems and more psychologists were needed in schools.

"Schools aren't properly equipped to support and understand mental health behaviors and triggers," she said.

"Focusing on the early primary school years will much better equip students for the transition to high school. Trying to get my child ready for high school is almost insurmountable now given how late the treatment came."

MCRI Professor Harriet Hiscock said having a greater understanding of the developmental trajectories of the major mental health disorders from childhood to adulthood was critical to informing the timing of treatment and intervention efforts.

"Given the COVID-19 pandemic has further compounded mental health problems, it's even more vital to assess for mental health problems in young children and to design, evaluate, and implement prevention and early intervention programs for children prior to adolescence," she said.

"Mental health supports for primary school aged children need strengthening and frontline providers such as GPs, nurses, pediatricians and child psychologists require upskilling to manage child mental health concerns."

Professor Hiscock said a "community of practice" pilot in Melbourne's west and north was aiming to improve the capacity of primary and secondary care clinicians to identify and manage infant, child and adolescent mental health presentations, reduce pressure on specialist services and support earlier access to treatment and care.

The findings come after a recent survey by MCRI found fwo in five young people experienced mental health problems and one in five had suicidal thoughts during the COVID-19 pandemic last year in Victoria. School closures also saw four in five teenagers report an increase in school-related stress.

Researchers from the Institute for Social Neuroscience, University of Melbourne, The Royal Children's Hospital, Deakin University, Women's and Children's Health Network in North Adelaide and the University of Adelaide also contributed to the findings.