I'm very accident-prone, and injure myself regularly, but most of those scars usually go away after a few days / weeks, depending on how bad the injury was.
Although I have a permanent scar on my left knee. I was about four, and was on the down escalator with my mummy, saw nobody in front of me, so I decided it'd be fun to run down as fast as I could. I tripped and fell on the actual escalator, then at the bottom part where the escalator goes under the floor, my knee was like getting sucked in with it, and that grazed it really badly, to the point where it shed a lot of skin and bled like maaad.