Growing understanding that mental health disorders including anxiety and depression are just as real for children under five as they are for adults is driving a new push for concerned parents to seek help.
Leading the way, the $11 million national Healthy Kids Check program was expanded in July to provide voluntary checks for families through their GP, with referral to mental health services as needed. An estimated 27,000 children are expected to be identified for extra support over the five years of the program.
About half of lifetime mental health problems have their roots in childhood but early detection can prevent problems becoming worse and reduce the chances of poor mental health as adults, according to child development experts.
However, it is still a controversial area for some in the field, with many questioning whether infants or very young children can be accurately diagnosed with a mental disorder.
Furious debate broke out among academics and practitioners earlier this year with the expansion of the Healthy Kids Check program to now screen three-year-olds for early signs of mental illness.
Kidsmatter, a national early childhood mental health initiative, estimates between 4 and 14 per cent of children aged 18 months to three years have mental health problems including anxiety, social withdrawal and high levels of aggression.
Child psychiatrist Caroline Goossens, from Child and Adolescent Health Services, said mental distress among infants and young children was a real concern.
"We know in fact that infants and young children can get quite depressed, they can certainly get very anxious and they can express a lot of distress through what we call externalising behaviour as well, especially as they get a little older, with defiance and aggression," she said.
She said parents should not allow fear of their child being "labelled" to prevent them from seeking help.
Medication was not used to treat this age group and interventions could quickly help children back on track. A number of measures in children could predict difficulties later on, Dr Goossens said.
"We know young children with significant behavioural problems and aggression, if unaddressed, can have significant difficulties at school and in relationships with others. At the most severe end these children could go on to be part of the juvenile offender population."
Other concerning behaviours could include emotional withdrawal and separation anxiety, all of which could be normal at certain stages, but became a concern if they were frequent, intense, lasted long periods and were age inappropriate.
"Small children can present with signs of trauma as a result of abuse and neglect and too many are not receiving the mental health assessments and interventions they require to recover and thrive in the future," Dr Goossens said.
Toxic stress that is a result of family stress or turmoil plays a key role in children developing mental distress.
An accurate diagnosis for very young children, especially those four and under, was difficult, Telethon Institute for Child Health Research population sciences head Steve Zubrick said.
Beyondblue's general manager of research, childhood and youth, Brian Graetz understood people might worry about "pathologising fairly normal behaviours that are going to be transient".