The children of women who smoke during pregnancy are predisposed to experimenting with tobacco at a young age, claim researchers.
Among 10-year-olds who said they had experimented with cigarettes in a survey, the majority had mothers who had smoked while pregnant.
The researchers at the University of Pittsburgh say the link may be caused by damage done to the foetus by tobacco smoke while in the womb. Earlier studies have shown that children exposed to smoke before birth suffer development problems, including attention deficit disorders.
Dr Marie Cornelius, who led the research, said: "The role of prenatal tobacco has been largely overlooked as a risk factor for the development of tobacco use among youth. "Our findings indicate that foetal exposure to tobacco may have a significant impact on early initiation of tobacco use in children."
The researchers questioned almost 700 10-year-olds, more then half of whose mothers smoked an average of 15 cigarettes a day during pregnancy. Among the 47 children who said they had smoked, most had been exposed to tobacco in the womb. Research in animals suggests that damage to the brain during pregnancy could be one reason why children go on to smoke.
Dr Cornelius said: "The resulting central nervous system damage may later be expressed as impulsivity, inattention, aggression, depression, and/or anxiety and may create a vulnerability in the child that could contribute to poorer adjustment and a greater likelihood of early initiation of tobacco use."
Spokeswoman Amanda Sandford said: "I would have thought if children live in an environment where the parents are smoking, that would be a stronger factor. "It is possible that there may be some physiological effect when the foetus is developing so the child becomes predisposed to smoking because they are accustomed to the smoke component.
She said it was important that both mothers and fathers gave up smoking during pregnancy and did not start again once the child was born.