The data come from the UK Obstetric Surveillance System, with funding from the National Institute for Health Research and the National Perinatal Epidemiology Unit.
A major study on the findings is due to be published by the British Medical Journal next week.
Professor Marian Knight, of the University of Oxford, the lead on the study, told The Telegraph that while she could not be certain she thought all six babies had caught the virus after being born.
She said: “All we can say about these six babies is that they were neonatally acquired and, if I were to be putting my finger on anything, it is more likely it was acquired around birth rather than before birth.”
Of the six babies who contracted the virus, only one needed to be treated in a neonatal unit, Prof Knight said.
There had been no tests of amniotic fluid, umbilical cord blood or the placenta, which would tell doctors whether the virus was passed to the babies in the womb.
Prof Knight and her team are already looking at a wider study of a bigger group of babies to see how they have contracted the virus. She said there was no evidence that babies were catching it through breast milk.
“For me, this study does not give us strong evidence of a major health impact for babies of coronavirus such that we should be advocating separating them from their mums or stopping mums from breastfeeding,” she added.
“We have absolutely no evidence that it is in breast milk – all we know is that it is in respiratory droplets. So the advice from the Royal Colleges of midwives and obstetrics is that women breastfeed with a mask on, because we know that cuts down on any droplets spread.
“These babies had a positive test at a very young age… [but] it is very unlikely that breastfeeding is a mechanism of transmission for these babies.”