Birthmarks on infants are fairly common. They are usually benign meaning they aren’t a sign of cancer, infection, or other serious condition. They won’t harm the child or cause other problems. They may go away as the child grows.
There are some skin lesions in children that do have significance. Cafe-au-lait lesions are flat with a creamy brown color. Cafe-au-lait is French for milk with coffee since that’s the color of the skin changes.
One or two cafe-au-lait spots may not mean anything. More than five requires further assessment. A neurologic condition called neurofibromatosus may be present. Or an allergic condition called uritcaria pigmentosa can present with skin changes that look like cafe-au-lait spots.
There is also a condition called Cobb syndrome associated with what look like port wine stain birthmarks. These skin changes may be a sign of underlying malformation of the blood vessels. Such a birthmark along the spine may signal bleeding and spinal pathology.
The fact that your grandchild has large birthmarks in more than one place may not mean anything. But your peace of mind is important and further evaluation won’t hurt. Consider asking for an MRI of her spine to rule out any other neurologic problems.