It is time,
The Ramban you cited is describing what is commonly referred to as “ruach hakodesh” not the Nevuah of Tanach wherein someone received a communication from Hashem (in fact that is the entire point of the Ramban). The Gemara the Ramban is commening on also says ?”? ????? ???? ???? ??? ????? ????? ????? ?? ??????? ?????? ?????? ????????? ??????. Obviously, it doesn’t mean that children and simpletons have nevuah in the same sense that Shmuel HaNavi did.
What is your source for that quote from Rav Shneur Kotler? I have never heard it before and it sounds fishy.