A turtleneck or a scarf is traditional. If it were mine, I'd
paint a little makeup on it (cover-up stick, probably) out of
modesty, just enough to pretend I was hiding it, and go ahead and
let it show. My kids are old enough to deal with it.
But if there are parents in the picture and discretion is
indicated, try the high collar. And next time make visible areas
off limits.