If their offspring then start using the devices at an early age, the chance of problems climbs to 50 per cent, according to researchers.
They found those exposed to mobile phones in the womb had a 30 per cent rise in behavioural difficulties at the age of seven.
But those exposed before birth and in their childhood, were 50 per cent more likely to have behavioural problems than those exposed to neither.
Children who used mobiles, but were not exposed in the womb, were 20 per cent more likely to display abnormal behaviour.
The findings by researchers in California are likely to reinforce warnings that children should not use mobile phones.
However, some British scientists were sceptical, saying the findings may be due to lifestyle factors rather than mobiles.
In the study of 29,000 youngsters, mothers provided details of their lifestyle, diet and environment during and after pregnancy.
Information on their children’s health and mobile phone use was also recorded. Around three per cent of children scored abnormal on behavioural issues, with another three per cent ‘borderline’.
The study found that more than ten per cent of children exposed to mobile phones in the womb had mothers who spoke on them at least four times a day.
Nearly half of the mothers had their phones turned on at all times while around a third of children were using a mobile phone by the age of seven.
The findings published in the Journal of Epidemiology and Community Health mirrored an earlier study by the survey team.
Researcher Dr Leeka Kheifets said both sets of results ‘demonstrated that cell phone use was associated with behavioural problems at age seven years’.
The scientists said social factors, such as mothers paying more attention to mobiles than their children, were only partly to blame. Dr Kheifets added: ‘We are concerned that early exposure to cell phones could carry a risk.’
In Britain, Professor Lawrie Challis, a leading government adviser on the radiation effects of mobile phones, has gone on record saying children should not use them until aged at least 12. But more than half of under-tens own a mobile.
Patricia McKinney, emeritus professor of paediatric epidemiology at the University of Leeds, said it was difficult to see how mobile use could affect an unborn baby.
She said: ‘Exposure to radiofrequency radiation from mobile phones is highly localised to the part of the head closest. There is no evidence to suggest that other parts of the body are affected.
‘We also have no evidence that a pregnant mother’s behaviour is related to her mobile phone use and thereby affecting her baby.’
Professor David Spiegelhalter, from the University of Cambridge, was also ‘sceptical’ of the results.
He said: ‘One finding is that very young children who use mobile phones show more behavioural disorders. But is it plausible that the first causes the second?’
Professor David Coggon, from the University of Southampton, said: ‘The pattern of results suggests the increase in behavioural problems may have been caused by factors other than mobile phone use.’
In May, the largest study of its kind said that using a mobile does not appear to increase the risk of certain types of brain cancer.
The International Agency for Research on Cancer analysed data for more than 10,000 people and found no link between years of use and risk.