Are school bullies a product of sad moms? Mothers who suffered postpartum depression are more likely to see their children turn violent as they grow up. And the children of mothers who suffer repeated episodes of depression are at a higher risk of becoming violent, according to an 11-year study in South London that tracked children from conception.

The study, published in this month's Developmental Psychology, involves 122 families representative of Britain's contemporary urban population. Psychologist Dale Hay at Cardiff University in the United Kingdom and colleagues investigated the impact of postpartum depression on children. Mothers were screened for depression during their pregnancy, three months postpartum and periodically thereafter. When the children turned age 11, the kids--along with their friends and parents--were interviewed about violent behavior.

As expected, most children were not violent. Nonetheless, the children women who were depressed after childbirth were more violent than others. This was especially true for mothers who had more than one episode of depression after childbirth. At age 11, these children had greater difficulties with attentiveness and controlling their emotions. Fights often led to injuries and suspension from school. Boys were more violent than girls.

Researchers are at a loss to explain the link between maternal depression and childhood agression. There could be a biological connection between anger and depression. It is equally likely that depressed mothers raise aggressive children. "What is clear from this study," notes Hay, "is that the mother's mental state after childbirth is an easily identifiable risk factor for her child's intellectual and social development."