Symbolic annihilation is used to highlight the erasure of peoples in popular communication, including in children’s books, of course.
I only heard of this term this week, thanks to an article at Jezebel, but I’ve been aware of the concept for a while. Once you start noticing how few non-white characters exist in modern picturebooks, as well as the gender discrepancy (it’s about 70/30) you can’t stop noticing. And now I know what it’s called.
Symbolic Annihilation from Wikipedia.
Its correlate is Symbolic Glorification, for example sporting heroes in Western culture, or ethnic minorities but only on festive days, or of women on TV, so long as they’re under 30 and fit the Beauty Ideal.