I think she places too much importance on this:
"British children’s books have often taught other truths – that the best thing you can be is white, upper or middle class, and if you are a girl, quiet. "
Firstly, there are many exceptions. For example, Aravis in CS Lewis's The Horse and His Boy is neither white nor remotely quiet - she is aristocratic. The Telmarine descended characters in the later books in the series are (in our terms) mixed race, and this was one of the most successful chidlren's book series ever, written in the 1950s. The Family from One End Street (which i remember reading as a child) was published in 1937 and is about a working class family.
Even Kipling is better than the article gives him credit for "You’re a better man than I am, Gunga Din!"
I think some bias towards middle class[1] characters and settings is inevitable because authors are middle class and write about what they know.
"You can only be a hero, we have told children, if you have that kind of name: names licked clean by kings and queens."
BS, as a non-white kid growing up in 70s and 80s Britain I never felt this. The author thinks people can only identify with characters like themselves, which is condescending.
"That is changing now, albeit slowly: books such as Malorie Blackman’s Pig Heart Boy, Patrice Lawrence’s triumphant People Like Stars and Tola Okogwu’s Onyeka and the Academy of the Sun"
Three British authors!
[1] the British definition of middle class.