It's not just kids. When I was 14, my sewing teacher told me, offhand, that I would be passably pretty if it wasn't for my crooked knees. I had never thought about my knees before, but then all of a sudden I hated them. They really are crooked! It wasn't until a few years ago that I managed to go outside in something that didn't cover my knees.
And I have "meat curtains" as well. When they started growing out I was convinced something was wrong with me, that it was some weird form of cancer or something. I even thought about numbing myself with ice and cutting off the dangliest bits. (Okay, stupidest kid award goes to... 13-year-old Pip.) I second/third/four? the opinion that watching a lot of porn is very reassuring.
Now I like my dangly bits.