I think the point Wren is trying to make is that there is an argument to be made that a public school teacher expressing belief or nonbelief in fairies is just as appropriate or inappropriate as a teacher expressing belief or nonbelief in God. This is why "Hmm...I don't know...I can't prove it either way" is best. I can certainly see that it seems more rational to be careful about mainstream religious belief than belief in fairies...but in fact, from a truly fair POV, why? I also know people who believe in fairies, by the way. Really!
I'll point out that to a child, this all sounds equally fantastical and odd. My unchurched child went to Catholic preschool last year and was utterly mystified by some of what went on there, referring to the "cups of other people's blood" he encountered with a bit of anxiety.
