This 2014 human study found one way that an infant unconsciously recognized the emotions of the humans in their environment:

“The current study provides neural evidence for the unconscious detection of emotion and gaze cues from the sclera in 7-mo-old infants.

Wide-open eyes, exposing a lot of white, indicate fear or surprise. A thinner slit of exposed eye, such as when smiling, expresses happiness or joy.”

The basis for finding that the subjects’ responses were unconscious was that the researchers determined that displaying images of eyes for 50 milliseconds fell below the threshold of infants’ conscious awareness.

http://www.pnas.org/content/111/45/16208.full “Unconscious discrimination of social cues from eye whites in infants”