I've had one in the middle of my upper back for my entire life. I have a few moles and a distant relative with skin cancer, so I go get them checked at least once a year by my dermatologist. The cafe au lait spot has never been an issue. I've actually had other moles removed (for medical as well as cosmetic reasons), but the cafe au lait spot is still there, doc's never once mentioned removing it. I would tell your sis not to be concerned from a medical standpoint if her doc isn't. But if it's a large spot on the child's face, maybe she's also concerned about the appearance of it. I've had a couple removed from my face and neck just because I didn't like them...and my kids, as babies, would keep going for them. She should talk to the doc about having it removed if it's going to cause so much worry. She should be aware, that she'd probably be trading in the spot for a scar (face, neck and upper chest seem to scar a bit worse than the rest of the body), but since her child is still young, it will probably fade by the time he/she's an adult.