I must admit that every linguist and developmental psychologist I have talked to has insisted that this is wrong, but they have not given me a single source. I believe that they correctly quote the textbooks, but that the textbooks repeat the myth without evidence. Here is a survey. (ungated pdf, but large)
I can definitely vouch for the pronunciation part, but is the rest really true? Source?
I must admit that every linguist and developmental psychologist I have talked to has insisted that this is wrong, but they have not given me a single source. I believe that they correctly quote the textbooks, but that the textbooks repeat the myth without evidence. Here is a survey. (ungated pdf, but large)