KIDS want to avenge bad behaviour from the age of six, scientists have found.

This is the age that children want to witness those who are naughty getting their just desserts, something that is not present in younger kids.

New research published in the journal Nature Human Behaviour shows that while kids are kind and feel uneasy and want to help when someone is needlessly suffering, they have no sympathy for those they deem to deserve punishment.

Brisbane psychologist Judith Locke said it made perfect evolutionary sense to feel that baddies should get their comeuppance.

"When a child sees that actions have consequences it helps encourage them to do the right thing socially," Dr Locke said. "This is a helpful start on their road to good behavioural choices. It is a common message in countless fairytales that good triumphs and the bad guy loses."

Researchers from the department of social neuroscience at the Max Planck Institute for Human Cognitive and Brain Sciences and the Evolutionary Anthropology department tested children with a puppet show.

The six-year-old children's preference to reject rewards so they could witness the punishment of the anti-social puppet was significant. They even experienced pleasure by watching him suffer.

Younger children did not have the same reaction.

"It is important though, that when your child becomes more mature you encourage them to understand that not everything is fair and things are a little more complex than good and bad people and move them beyond an inaccurate perception that the world is always fair," Dr Locke said.

Five-year-old twins Harrison and Oliver Burstow have it all ahead but their mum Simone says they are already beginning to understand there are consequences for behaviour that is both good and not so good.

"I think they are definitely at the age where they understand repercussions," she said.

KIDS want to avenge bad behaviour from the age of six, scientists have found.

This is the age that children want to witness those who are naughty getting their just desserts, something that is not present in younger kids.

New research published in the journal Nature Human Behaviour shows that while kids are kind and feel uneasy and want to help when someone is needlessly suffering, they have no sympathy for those they deem to deserve punishment.

Brisbane psychologist Judith Locke said it made perfect evolutionary sense to feel that baddies should get their comeuppance.

"When a child sees that actions have consequences it helps encourage them to do the right thing socially," Dr Locke said. "This is a helpful start on their road to good behavioural choices. It is a common message in countless fairytales that good triumphs and the bad guy loses."

Researchers from the department of social neuroscience at the Max Planck Institute for Human Cognitive and Brain Sciences and the Evolutionary Anthropology department tested children with a puppet show.

The six-year-old children's preference to reject rewards so they could witness the punishment of the anti-social puppet was significant. They even experienced pleasure by watching him suffer.

Younger children did not have the same reaction.

"It is important though, that when your child becomes more mature you encourage them to understand that not everything is fair and things are a little more complex than good and bad people and move them beyond an inaccurate perception that the world is always fair," Dr Locke said.

Five-year-old twins Harrison and Oliver Burstow have it all ahead but their mum Simone says they are already beginning to understand there are consequences for behaviour that is both good and not so good.

"I think they are definitely at the age where they understand repercussions," she said.