Three and four-year-olds are more physically aggressive than most adults, new research has suggested.
Aggressive behaviour is natural in young children, researchers say
This is because children must learn to regulate their use of violence in the early years as they mature, child expert Professor Richard Tremblay says.
Whether or not children manage to do so depends on a range of environmental and genetic factors, he adds.
Those who do not are more likely to become aggressive adults, he will tell a Royal Society conference in London.
Professor of paediatrics, psychiatry and psychology at the University of Montreal, Prof Tremblay warned that physical aggression in children was a "major public problem".
Not only was it an indicator of aggression in adulthood but could also lead to other serious behavioural problems like drug and alcohol abuse.
Factors influencing whether a child's aggressive tendencies remain uncheck ranged from the type of parental care a child received to whether its mother smoked when pregnant.
"Research has shown for example that nicotine affects the development of areas of the baby's brain which are responsible for emotional control," he adds.
Physical aggression increased the most in the early years when human development was on "fast forward", he said.
During this time, "environment plays a very important role in the extent to which physical aggression develops or is controlled", he added.
Recent studies show that most children substantially increase the frequency of physical aggressions between nine months and the age of four.
At this age, children are exploring social interactions with their newly acquired skills in walking, talking, running, grasping, pushing, kicking and throwing.
Most of their interactions are positive, but conflicts - during which children learn that they can hurt and be hurt - become more frequent, the research says.
"Most children will quickly learn that a physical attack on a peer will be responded to by a physical attack, and that adults will not tolerate these behaviours," it adds.
And most will learn that asking for toys, rather than taking them away from someone, is less likely to result in a negative interaction.
Aggression is "rather a behaviour like crying, eating, grasping, throwing, and running, which young humans do when the physiological structure is in place."
But most youngsters learn to regulate these "natural" behaviours with age, experience, and brain maturity, regulating their needs to adjust to those of others in a process generally labelled "socialisation", it adds.
Prof Tremblay argues that identifying the factors which stop young children becoming socialised adults should help "preventative measures" to be developed.
"These should put an appropriate emphasis on the behaviour of parents as well as that of the child," he concludes.