However, the findings published this week also said that being looked after by grandparents does appear to help develop a baby's vocabulary, particularly for children who also have highly educated mothers.
Researchers suggested this could be because grandparents have more time to talk to children than other carers and are more likely to use grammatically correct sentences and to correct children's language.
Mothers who took part in the study reported that children cared for by their grandparents had more behavioural problems at the age of three than those who had been in nursery or had been looked after by a childminder, nanny or other member of the family.
The research involved 4,800 children whose mothers all worked when they were babies and are being tracked by the Millennium Cohort Study.
One in three of the parents surveyed had children who had been cared for by grandparents.
The study did not investigate why children looked after by grandparents have more behavioural problems but researchers highlighted previous studies that suggest that spending time in pre-school settings can help children develop the social skills to get on with their peers.
Co-author Kirstine Hansen said, 'A possible explanation is that grandparents are less mobile and less likely to take children to play sessions.'
Children who had attended nursery were also found to be more ready for school.
Dr Hansen added, 'This is almost certainly because nurseries and crèches are more likely to offer structure and content to daily activities with children and their staff are more likely to be trained, to have better facilities and resources and to provide more educational stimulation.'
The researchers said this finding was important because it suggested that childcare had the potential to reduce inequalities.
Early Childcare and Child Development by Kirstine Hansen and Denise Hawkes is published in the current issue of the Journal of Social Policy at www.cambridge.org.
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Nurseries 'better for babies' than grandparents' care
Babies who are looked after by grandparents have more behavioural problems by the age of three than those in nursery care, new research suggests. They are also less ready for school.