DS had an injury when he was 2 that required 2 stitches to mend a cut in his cheek, plus 7 stitches in his lip (2 layers of stitches in the lip, it was really deep).
He's 6 now. The cheek scar is completely gone, but I can still see a faint scar on his lip. It's not noticeable to most people, but I know it's there.
We did use sunscreen on him religiously, but it's tough to keep a layer of sunscreen on a toddler's lip. He also hated hats and would rip them off as soon as I turned around (there's no reasoning with a 2yo...). I expect that, along with the depth of the cut, is why we can still see the lip scar but not the cheek scar.