Q:

Cute as a button

Since buttons aren't particularly cute (IMO), where did this common phrase come from? I know it's old; I've seen it in 19th century literature.

A:

While I can't find any scholarly answers, most answers I'm finding say that 'button' refers to something pretty or attractive in a dainty way. After all, you're using the word 'cute' so you wouldn't be using it to describe a large, muscular man. This phrase would be best suited for a small child or flower.

CUTE AS A BUTTON - "cute, charming, attractive, almost always with the
  connotation of being small, 1868 (from the original 1731 English
  meaning of 'acute' or clever). Cute as a bug's ear, 1930; cute as a
  bug in a rug, 1942; cute as a button, 1946. Cute and keen were two of
  the most overused slang words of the late 1920s and 1930s." From
  "Listening to America" by Stuart Berg Flexner (Simon and Schuster, New
  York, 1992.)
Flexner may have an idea about the word "cute," but he provides no
  guidance on the question of how a button can be cute. The key to the
  issue is that it is not the button on a shirt that is meant here, but
  a flower bud seen in the popular name of small flowers, such as
  bachelor's button (q.v. "button" (n) in the OED, meanings 2 and 3).
The British version is "bright as a button". This makes sense if you
  think of a polished brass button. The phrase is really only ever used
  of small people - you'd say that a child, or maybe a small dog, was as
  bright as a button, but you'd never say it of a six-foot man. So the
  image is of a small sparky thing.
http://www.phrases.org.uk/bulletin_board/41/messages/652.html

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