A leading NSW Hunter Valley paediatrician and Children's Court magistrate provided a rare insight on Wednesday into how the heath and justice systems are failing vulnerable families.

Their evidence and submission, to a Senate inquiry into Fetal Alcohol Spectrum Disorder (FASD), paints an unflattering picture of a stressed and stretched paediatric health system, vast waiting lists, medical staff not equipped to properly treat patients and undiagnosed children in and out of the criminal justice system.

FASD, which the World Health Organisation calls the leading cause of preventable intellectual disability, is a range of incurable, but preventable conditions, caused by exposure to alcohol in the womb.

Newcastle Local Drug Action Team deputy chair, Dr Murray Webber, said many children with FASD were unable to access assistance due to lack of services and limited training for health professionals to diagnose the condition.

Dr Webber is a senior paediatrician who works at NSW Hunter New England Health's only outpatient paediatric clinic for children aged two to 12 with multiple and complex developmental disorders.

"Unfortunately, the demand for our service far exceeds our capacity to respond, and there is currently a wait of over 12 months for a multidisciplinary assessment," he said.

"There has been no enhancement of our service to meet the increasing requests for developmental assessments, or for specific FASD assessments."

The clinic, that has 1.6 full-time equivalent paediatricians and two paediatric trainees, receives about 350 referrals each year.

More than 20 per cent of referrals are Aboriginal children and a "high percentage" are in out-of-home care.

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There is no multidisciplinary developmental paediatric service for children over the age of 12 in the Hunter Valley.

Dr Webber said too many children with FASD were being misdiagnosed or slipping through the cracks with no help.

"There is a much larger demand than we can supply," he said.

"An increase in referrals for assessments, we are seeing that, but we don't have the increased capacity we need to provide the kind of care these families need."

The inquiry heard the lack of diagnostic services was having a "flow on effect" to the Hunter Valley's Juvenile Justice system.

Newcastle's Broadmeadow Children's Court Magistrate Nell Skinner said with no service available in the Hunter, there was a two-year waiting list for adolescents to be assessed at a developmental paediatric clinic outside the region.

"We have the capacity to delay court a little, but we're not going to delay it for two years," she said.

The inquiry heard that undiagnosed offenders suffering from FASD, who could be diverted from the criminal justice system, were not being identified.

"We have so many children with behavioural disorders that could be put down to FASD if someone had the capacity to assess them," Magistrate Skinner said.

Newcastle Local Drug Action Team is pushing for funding to establish a "one stop shop" FASD diagnostic clinic in the region.

Magistrate Skinner said young offenders were not screened for FASD, that results in permanent brain damage, or other impairments by the courts.

She said studies revealed an "alarming incidence" of impairment amongst juvenile inmates.

"There is a risk that some young people are not appropriately diagnosed, resulting in a process they do not understand, with orders they will breach," she said.

A 2014 study of eight NSW juvenile detention facilities found 45 per cent of detainees had "borderline or lower intellectual functioning".

"We recognise that the prevalence might be much greater than we think but we don't currently have the capacity to do an assessment and to follow through on it," Magistrate Skinner said.

"And that is something that could change if we want to try and improve some outcomes."

Following a two-day FASD training program in 2018, funded by an allied health grant, Dr Webber said clinic staff had completed 25 assessments and half of the children were diagnosed with FASD.

"There is still a long way to go before all the relevant agencies and services have the knowledge and skills required to help identify and care for children, and adults, with FASD," he said.