The national survey of 5500 children aged 9 to 13 highlighted the significant gap in wellbeing between mainstream kids and those who have a disability, are Indigenous, are young carers or from poor backgrounds.

Thirty per cent of children fall into one or more of these marginalised groups, and they rate their health worse, are less happy at school and have lower levels of family cohesion than their peers. Children with a disability are the worst off overall.

"There is a lot of diversity in wellbeing among young Australian children," Flinders University associate professor Gerry Redmond, who led the study, said. "We need to focus on why some children are doing a lot less well than others."

The gap between marginalised and mainstream kids is particularly pronounced by the time they reach year 8.

The Government-funded Australian Child Wellbeing Project surveyed children in years 4, 6 and 8 from 180 schools. Students were asked about their family, living arrangements, school, health, friendship, material wellbeing and bullying. It is the first national survey of children in the middle years, and the findings will be presented at the Australian Social Policy Conference on Monday.

Overall, most children report high life satisfaction and are optimistic about their future. More than 90 per cent of children are in good health. Children nominated family as the most important factor for having a good life, followed by health and friends. Those with a big support network were healthier, more engaged with school and less likely to be bullied.

However, some children are struggling more than their peers. One in five kids report being bullied once a week, with year 4 students experiencing the highest levels of bullying. Bullying included being ignored, being teased, having lies told about them, and people ganging up on them.

Children from marginalised groups were more likely to be bullied, and those with a disability the most bullied of all. The more often children are bullied, the more likely they are to miss school.

"I get the impression, talking to teachers, that this kind of non-physical bullying, like exclusion and telling tales, is extremely difficult to counter," Professor Redmond said.

Sixty per cent of all children who were bullied reported two or more health issues, including frequent headaches, stomach aches, dizziness, feeling nervous, or having difficulty going to sleep. These complaints are often symptoms of stress.

A quarter of young people have a family member who has a disability, chronic illness, mental illness or drug or alcohol addiction. These young people experience significantly more health complaints than their peers.

"These health problems may be associated with worries about their family, and their direct caring responsibilities," Professor Redmond said. "They're worrying about these things that are normally seen as adult issues."

Mainstream kids score an average life satisfaction of 85/100, while marginalised children score between 64 and 70. Similarly, mainstream children have a health score of 90/100, compared to marginalised kids, who score between 72 and 81.

Professor Redmond said his study provided the hard evidence policy-makers and schools need to act to better help these kids. "Young people in these groups are marginalised, but they actually comprise a large proportion of all young people," he said.

"This should give policy-makers extra impetus to reduce the disadvantage they experience, and improve their lives."