Research from the Centre for Literacy in Primary Education highlights the problem of the lack of diversity in children's books.
Its 'Reflecting Realities' report found that only 7% of children’s books published in the UK from 2017 to 2019 featured characters from BAME backgrounds, though there are signs that the proportion is slowly increasing. By comparison, 34% of the UK's school population in 2019 were of BAME origin.
There is more data and information about the 'Reflecting Realities' project here.