It's not just their unfiltered honesty. For me, it's that they're small little destructive germbags that just happen to be the right height for me to turn and hit their eye with my hand or elbow if I don't see them (which I usually don't, since they're far below eye level). The way they walk and run also just freaks me out. Like, do they not have knees? They also tend to even have no concept of volume control and their voices usually hurt my ears. Kinda hard to keep your cool when you feel like your eardrums are being stabbed over and over again.
All in all, they're too stressful for me to ever find cute. I like having my anxiety at a manageable level--like, you know, a level where deep breathing isn't painful. Not even exaggerating there. I worked at an afterschool program for a few months and I would get lightheaded around the small children because my body would automatically switch to shallow breathing.