DS was born with 'stork-bites' between his eyebrows and on the back of his neck, and a mongolian blue on his bum. The stork-bites faded within a couple of years (I don't remember exactly, but the ones on his neck were gone by 1yo, and on his face by 2yo) but they used to get very red when he cried, even after they had apparently disappeared. The blue is still visible, but is much faded. He also developed cafe-au-lait marks after being exposed to summer sunlight.
I used to worry a lot, not about the marks themselves because I knew and believed they would fade, but about whether he would develop a strawberry mark. I have one, which appeared when I was a few weeks old and grew very large indeed. It looked like I had had a very large over-ripe strawberry squashed onto the edge of my eye. It probably started shrinking and fading when I was 6 or so, and was virtually invisible by the time I was 16. Oddly enough, although I was often bullied at school, my birthmark was never the subject. I myself was never bothered by it, and nobody else seemed to be, either. I was often asked about it, usually by 'new' people who generally assumed that it was an injury. When I asked my mum how come they weren't bothered by my mark she said that they had decided that if they weren't bothered then no-one else would be. It seemed to work!
If my mum saw another mother with a baby with a strawberry mark, she used to embarass me by dragging me up to show how the mark would fade (she still does that! ) to reassure the mother. I didn't care for it then, but now that I'm a mother myself, I do it too!