Hi, R.,
My 20-month-old son has had a congenital nevus (a mole) on his leg since he was born. It is black, flat and slightly bumpy but not hairy. It now measures approx. 3/4"x2" and will expand he he ages. I estimate that if we leave it alone, it will expand to at least 2"x4". I took him to a ped. dermatologist, who said that it will probably not lead to melanoma, but that we could get it removed when he was old enough to sit still (maybe 6 or 7)to lower the odds of him developing this disease. He will probably need three operations while under local anasthesia to remove the mole. He will have a large scar, but it will still probably look better than a very large, dark mole. Obnoxious people still repeatedly ask us what's wrong with him. REALLY annoying.
I don't know much about your son's case, but if I were you, I would keep his head covered with a hat or sunscreen (as you have been) and just relax until your son's appointment. You are doing the right thing.
Good luck,
Lynne E