what are the pros and cons about this book being written from a third person point of view and how would it be different if it were written from one of the characters point of view

The third-person omniscient narration is straightforward. The narrator has an uncluttered and complete view of everything that's happening in the story. More importantly, the narrator can more easily portray the thoughts of any given character at any time. For instance, sometimes the focus is exclusive to Lucy. At other times, the focus is entirely on Edmund, such as when he first encounters the White Witch. And sometimes, neither of the younger children are around at all, they're left out so that we can observe conversations between Peter, Susan, and the Professor.

I love this point of view and don't see any "cons" to its use. Things that would have changed if one of the character's points of view had been used would have been the author's ability to skip back and forth between events. With the use of the third person, Lewis has enabled the reader to visualize the whole picture rather than simple pieces.