Let's see...When I was about 2 and a half, I snuck out of bed, went down to my parents, and tripped over a small fireman car my brother had been playing with - fell with my head straight o nthe sharp corner of a cupboard. That was 5 stitches, directly in the middle of my forehead.
Then, when I was about 8, I was at a children's party, and even though they had told us explicitly not to dance on the tables, well, errr, I fell off the table, with my head straight on the sharp corner of another table. That gave me a swollen bump that still hasn't disappeared.
I had a lip gash once that simply wouldn't heal, and even though it's healed now (after about 14 months) it's permanently thinned one side of my lips.
When I was about 8 or 9, I was a wimp and my brother was big and strong, so I took one of those arm-strength-thingies with some elastics in between two handles (something like this, but with elastics instead of springs
Of course, me being the young weakling I was, I stretched them allll the way out, only for one side to slip from my grasp and smack me across the face. That's 4 stitches on the
other side of my lips.
All in all, eh, I don't look the worse for it
Anyway, by far the most noticeable one is the bump on my forehead. When I've tanned a bit or so, I'll still get people asking if I recently bumped into something, because that makes it stand out more. The rest, eh. A small, non-invasive scar doesn't detract from beauty at all; there's a reason women had "beauty spots" on the 19th century. Symmetry is pretty, too much symmetry is bland. Cosmetic surgery for any little thing leads to things like human Barbie, which no-one finds attractive.
If it's a serious scar, really altering the facial structure, that's one thing. If it's just a small line, even a bit crooked, I certainly wouldn't do anything at this age - as Stienman's pointed out, early cosmetic surgery will often have negative long-term effects, necessitating further operations to keep it pretty - as scar tissue around such surgery tends not to grow along with the rest of the body properly. Unless it's a horrible disfigurement, he's probably better off leaving it like this 'till at least his teens - if it's still noticeable and he feels it detracts from his looks and/or he gets made fun of for it, it'll be easier, probably cheaper, healthier and a more conscious choice to remove it at that time.