The (paraphrased) original question still remains valid and open; Have US children fallen behind the rest of the world to the extent they cannot read books and assimilate information to the extent others can? I think we have to admit the answer may be yes.
That was my original point. The author alleges he was told that his books are too "English" for American kids, whatever that is supposed to mean. But kids from other countries, including China, which has a totally alien language and nearly a totally alien culture, were able to to appreciate it. So why would American kids, who wouldn't even need to have the book translated from the original, and have a very similar culture, not be expected to be capable of assimilating the contents?