I remember the first time the kid nearly took a dive off the sofa arm. There was this pop sci/parenting factoid in my head that a child had this innate perceptive ability to avoid danger. Some scientist somewhere had done some study that showed that kids placed on a solid table with a glass cutout--i.e., a situation where visual cues all pointed to a dangerous clif--reacted by... see, I could never remember if they avoided the edge because it looked like a cliff, or if they crawled right across because they could discern that it was safe. Neither result would provide much comfort, though, if your little Strawberry Shortcake misjudges her center of gravity the first time she peers over the edgeand lands right on her giant bobble head.
Anyway, back then, I Googled around about topics related to proprioception [heh], and came across the work of Dr. Karen Adolph, a psych professor at NYU who specializes in early childhood development of perception and motor skills. The paper that was most fascinating to me at the time [so interesting, I was sure I'd posted it here... oh well] was "Specificity of learning: Why infants fall over a veritable cliff." [pdf]
In a series of experiments, Adolph and her colleagues discovered that kids had to relearn their whole sense of movement, perception, and balance for each developmental stage: sitting, cruising, crawling, walking, etc. Very interesting stuff. And now she has a book [chapter] coming out, too.
Karen E. Adolph, Infant Learning & Development [psych.nyu.edu]
Baby&Child@NYU: The Infant Action Lab [psych.nyu.edu]