Up to half of Australian children could be engaged in cruelty to animals and be capable of serious violence against humans, a leading criminology expert said.
Professor Paul Wilson, a criminologist and forensic psychologist at Bond University, will present a paper on the relationship between cruelty to animals and criminal behaviour in young people at an RSPCA seminar in Canberra this week.
The paper shows a worrying link between children who are cruel to animals and future, more violent crimes.
A 2002 study in Italy showed up to half of school-aged children had been cruel to an animal or animals.
"Cruelty to animals is a far more serious problem than first realised," Professor Wilson said.
A remarkable number of serial killers and mass murderers, Martin Bryant among them, had a history of animal cruelty.
"Paul Denyer, who killed three young women in 1993, disembowelled his neighbour's cat and cut the throats of kittens," Professor Wilson said.
"I am not saying it is the cause of serial killing, but it is a strong indicator."
There were several reasons why children would be cruel to animals, he said.
"There could be problems in the home like domestic violence or child abuse. It could be because of peer pressure or it could be the child is just sadistic."
Jo Hatch, of the Children's Protection Society, said there were different levels of animal cruelty.
At one end of the spectrum there were children who stomped on bugs and killed snails and other creatures.
"As it progresses there could be a child who teases the family pet, pulling its tail until it cries," Ms Hatch said.
"Often this child will stop when a parent or the animal signals distress."
But others could take it a step further, and seriously damage an animal.
The Children's Protection Society has started a pilot project for children who are cruel to animals.
A hotline opened earlier this month where children younger than 12 who are cruel to animals can get professional help.
The hotline number is (03) 9458 3566.