Man Singh, ‘What Babies Understand About Adult Sadness’, http://www.npr.org/sections/health-shots/2015/06/12/413917929/what-babies-understand-about-adult-sadness, Npr (JUNE 12, 2015).
By the middle of their second year of life, it turns out, babies do understand that a stiff upper lip can be appropriate in certain situations. (…) By 18 months of age, babies have a fairly sophisticated understanding of human emotion. (…) Infants are making an association between events that happen and emotions. (…) Infants learn a lot about their own emotions from those around them.
Sabrina S. Chiarella, Diane Poulin-Dubois, “Aren’t you supposed to be sad?” Infants do not treat a stoic person as an unreliable emoter, Infant Behavior and Development, 2015, doi:10.1016/j.infbeh.2014.12.007