I generally never mess with kid Sims' looks because it would ruin the surprise of how they'll grow up, and I want to see what their teen and adult selves will look like without my meddling. However, I voted "other" because there is one thing I will change that isn't looks, but it drives me bonkers when it happens: There is a certain voice that sometimes happens in kid sims, that I cannot S T A N D hearing. It makes me want to crawl out of my own skin. It's this extremely sassy, unpleasant voice and the kids affected talk in it all the time, not just when being sassy or teasing or whatnot. I couldn't be around a kid who sounded snide and jeering every second of every day.
So I change that if it happens, to alleviate the growing urge to end them.
About looks though, I had a Sim whose looks were negatively affected because he bore a genetic resemblance to his Reaper father that played out weirdly: he seemed to have inherited the coloration his dad must have had for whatever he would have been if he hadn't been a reaper (because the kid was light-skinned and ginger-haired, definitely didn't get that from the Goth side), but he got the strange, stylized face all Reapers have under their hoods if you change their clothes in CAS. So he grew up with the over-large, round eyes, delicate rounded features...kind of a baby-face with too-large eyes effect. It was strange, and impressive, and different. But not what anyone could call attractive. But I left it, because it reflected his unique heritage, and anyone can be stereotypically attractive, but not just anyone can be a Reaper/Normal Sim hybrid offspring.
