Few children grow up to be violently aggressive, but those who do tend to have physically abusive parents, according to this longitudinal study from Harvard University. Race, gender and family income had little effect on kids' likelihood of fighting, lashing out against peers, or attacking with weapons. But children who are physically punished at home and are socially withdrawn, distressed in new situations, and anxious about making new friends are at high risk for aggression. Researchers also found that being victimized by peers led to aggressive fantasy, which in turn predicted violence.
http://www.gse.harvard.edu/news/features/fischer08212002.html