Women who smoke while pregnant are more likely to have low birth weight babies, but a new study also says the children are more likely to be violent when they are toddlers.

The researchers from Canada and the Netherlands found the risk was even greater for low-income women.

"Mothers-to-be whose lives have been marked by anti-social behavior have a 67 percent chance to have a physically aggressive child if they smoke 10 cigarettes a day while pregnant, compared with 16 percent for those who are non-smokers or who smoke fewer than 10 cigarettes a day," said author Jean Seguin, of the Universite de Montreal.

But for women above a certain income line, there was only an 8 percent greater chance that a smoker would have violent children.

The findings were based on a long-term study of 1,745 children in Quebec. The children were studied from age 18 months to 3½ years. The youngsters were considered violent if their mothers said they were quick to hit, bite, kick, fight and bully others.

The study was published in the journal Development and Psychopathology.