My DD is coming up on two and in the last few months I noticed a little white mark just above her chin, like a circular scar. I don't think she's ever injured herself there, but she did have a chicken pock there so I presumed it was that. But she's napping on me now and, having a good look at it, it's now a thin white line about 5mm long. Looks for all the world like a scar but I'm certain she's never had any sort of injury there that would have caused it. Any ideas?