A.B.
Sounds like a scar to me. Kids don't have to have a big accident to get them. When I was born my sister stuck her head in my bassinett and I scratched her under her eye, still has the tiny scar she's 46 now. She could have scrartched herself and with exposure to the sun, even with SPF it made it darker. I wouldn't worry about it. Maybe get some Mederma, the scar cream and see if it'll fade a little.