Can you please explain the quote "Kids think with their brains cracked wide open; becoming an adult, I've decided, is only a slow sewing shut".

Children are eager to learn about anything at least most of them are. Remember they have little past knowledge stores to build on.

I think the education systems including college, tend to blinder the students after a while. An example was given by a noted science and science fiction writer, it may have even been Isaac Asimov, wherein a group of professionals were tring to decide how best to solve some involved equation. The son of one of them came in who was only in college a year or two, took a look at it and produced the solution immediately.

A few years later as a test after he had graduated his dad asked him to solve the same equations again and he was as stumped as the original group.

I think that as you go on and get involved in your discipline, unless you always keep an open mind, and taking any doctrines as maybe's not as facts you can stay open. But it is obvious from the infighting in the scientific community against any new ideas that most of the "scientists" are as closed minded as say religious fanatics.  They always want to follow the "party line" even after it has been proven to be false.

I know of such a case in the psychiatric community where a very few vocal minorities are attempting to get the new DSM-V written to reflect their erroneous ( in the minds of most of the others) views.