as counting Pinhead Angels, I may also see where there is a possibility of creating some understanding between the two groups.
Your Santa example is near perfect.
Suppose the child actually met the real Santa, not a storefront Santa, not Macy's Santa, not even Edmund Gwenn Santa, but the realy McCoy. In that case, even as the child matured he or she would still believe in Santa.
The rest of us may not have met the real Santa so it's perfectly reasonable for us to doubt the account, and there is absolutely no way that the child can prove his belief (he did get his Captain Midnight Glow in the Dark Decoder Ring but it was from Post, not Santa so it really isn't much evidence).
It is a reasonable assumption though that if one did meet the real Santa, then it would be hard to later not believe in the experience. It is equally reasonable to meet Edmund Gwenn who is enough like our vision of Santa to fool any child, and later realize he is nothing but a kindly old man with a beard.
The existence or non-existence of GOD will be proven beyond a shadow of a doubt, but unfortunately, not under conditions where that knowledge can be disseminated.
Aslan is not a Tame Lion