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.

You can read more [here][1].


  [1]: http://www.answerbag.com/q_view/184286#ixzz1xyWiXn5n