I'm bringing this back up to the top because this is a GREAT post...
...but also because it is important for parents to see, especially the bit about not encouraging makeup or encouraging covering it up, like it's ugly or something to feel ashamed about.
I think that a lot of the confident attitude I have regarding my own rather large PWS (much of my right leg) has a lot to do with how my parents regarded it - which was... not at all. Seriously, nobody ever brought up my birthmark, I never had it treated, never saw a doctor for it - it was just there, a curiosity. People said all kinds of stupid things to me over the years, but most of it was just because they were curious about it. Mostly, I'd just shrug it off and say, "It's a birthmark. It's not a rash, it's not contagious, and it doesn't bother me." Once people knew what it was, it wasn't so scary or weird, and (Your piranha story made me laugh - I once convinced a particularly ignorant person I'd been trapped in a burning building!)