The nice parents do get stomped on by a rhinoceros at the beginning of the book, I was always rather disturbed by that. On the other hand, once I read past that sentence I have always deeply loved that book.

Who exactly is/was banning these books (schools, libraries, cities, states, countries?)

How on earth is Shel Silverstein objectionable?

"A genuine anteater,"
The pet man told me dad.
Turned out, it was an aunt eater,
And now my uncle's mad!