Final answer:
Shelley and Julie are discussing their infants' temperaments, which are innate traits influencing their behaviors and reactions. The terms 'fussy' and 'easy' are indicative of difficult and easy temperaments, respectively, which have a biological basis and shape how children interact with their environment.
Step-by-step explanation:
Shelley and Julie are discussing their newborns' temperaments. Temperament refers to the inborn, genetically based personality differences that influence how infants think, behave, and react with their environment. Babies can generally be categorized into one of three temperaments: easy, difficult, or slow to warm up. An easy temperament describes children who demonstrate positive emotions, easily adapt to change, and can regulate their emotions. On the other hand, a difficult temperament characterizes children who tend to express negative emotions and have difficulties with adapting to change and regulating their emotions.
The discussions between Shelly and Julie about the fussy nature of Shelly's son and the easy-going nature of Julie's son relate directly to their children's temperamental differences. These temperamental traits are believed to have a biological basis and emerge very early in life, although they can be shaped by environmental factors and maturation over time.