N.B.
Great advice already...one more story. A young lady we know had a fall when she was about 3, cut her forehead wide open, had stitches (not done by a plastic surgeon); I don't think her parents did anything special, but over the years she "outgrew" her scar and you can barely see it. Mederma is good (after initial healing); definitely be zealous with the sunscreen; I'd probably use pure zinc oxide. It comes in colors now, so your son should love it!