More than half of those under 16 in the cities are now from black, Asian and other ethnic communities, they believe.
White children make up 47 per cent of the population in both cities, the researchers estimate.
The figures, which are expected to be confirmed by this year’s census, mean that for the first time white children are a minority group, although they are the biggest single ethnic group.
Education authorities say many different languages are being spoken in Birmingham schools (Picture posed by models)
The report estimates that in 2006 53 per cent of children under 16 in Birmingham, Britain’s second biggest city, were from white families.
It also forecast that the proportion of children aged under 16 who are from ethnic minorities will rise to about 64 per cent by 2026, while the proportion of children from white families will be 36 per cent.
In Leicester it is predicted that children from white families will make up 31.8 per cent of under 16s by 2026.
The predictions are contained in reports by the Cathie Marsh Institute at the University of Manchester. The Birmingham report was commissioned by Birmingham City Council while the Leicester estimates are from a student’s dissertation.
At the time of the last census in 2001, 70.4 per cent of Birmingham’s population of all age ranges was white and 29.6 per cent from a variety of ethnic backgrounds, dominated by those with Asian, Caribbean and African origins.
It is predicted that by 2024 no ethnic group will form a majority. At present the total population of the city is just over one million.
In Leicester, white British people made up 60.54 per cent of the population at the time of the 2001 census.
More than half of children in Birmingham will be from black and Asian communities, making white families a minority group, a report said today
Professor Ludi Simpson, who led the research team, said: ‘In Leicester and Birmingham, the white group will remain the largest by far – though it will not account for a majority of the population as a whole.
‘These and most other cities are already diverse with many different ethnic minorities.
‘Indeed it is indisputable that whether the whole of Britain or its city districts are considered, there will be more cultures represented in more equal numbers than in the past.’
The findings for Birmingham chime with Department for Education figures released last January.
They showed that 43 per cent of children at Birmingham’s primary and secondary schools were white. Out of 148,900 pupils attending council-run schools, 63,800 were white.
The 2011 census is being conducted in March, when 25million households across England and Wales will be required by law to answer a range of questions including who is registered as living at a property, their age, their education and their ethnicity.
The results, the first official figures since 2001, will be announced later this year.