I first read the Narnia books as a child, too, and I didn't spot the Christian allegory either. This is probably just helping your theory, though, because I also have atheist parents. Finding out they were meant to be Christian allegory diminshed the books for me, though I did still enjoy them when I re-read them all (in English for the first time) in my mid-twenties. I haven't really revisited them since.

Actually, what has inspired me towards re-reading them (but my list of books to read is so long it is not likely to happen any time soon) is reading Neil Gaiman's "The Problem of Susan", where he shows us a grown up, retired Susan. It is not a pleasant tale, and I am not sure I either like or fully understand it, but it does a good job of pointing out how unfair Aslan's rejection of Susan is.