bb has a birth mark at the ankle area. quite big patch. like blue black. will it be visible as they grow up? afraid will be ugly for girls...

My 4.5yo still has it even though slightly faded. People tell me it will disappear but most of her marks are still there. She has on her back, knees, ankles and back of her hands. "Mongolian spots are very common in any part of the body of dark-skinned babies. They are flat, gray-blue in color (almost looking like a bruise), and can be small or large. They are caused by some pigment that didn't make it to the top layer when baby's skin was being formed. They are harmless and usually fade away by school age. In most cases, no treatment is needed for the birthmarks themselves." Quote from www.webmd.com