The Development of Individual Physically Aggressive Behaviors From Infancy to Toddlerhood

In the present investigation, we studied the development of 6 physically aggressive behaviors in infancy and toddlerhood, posing 3 questions (a) How do the prevalences of individual physically aggressive behaviors change from 8, 15, and 24 months? (b) Are there groups of children who show distinctive patterns in the way individual physically aggressive behaviors develop over time? (c) What are the behavioral pathways leading from 8- to 24-month acts of physical aggression? Mothers and fathers (N = 272) from a moderately at-risk population reported on their children's physical aggression at each time point. The results revealed the commonality of physical aggression at all ages studied and the diverging developmental patterns of individual behaviors. Some physically aggressive behaviors became less common (e.g., hair pulling), while others became more common (e.g., hitting), with age. Roughly 42% of the children exhibited an increased propensity, relative to their peers, to aggress at all ages. Kicking, biting, hair pulling, and pinching/scratching at 8 months were the first steps on behavioral pathways leading to physical aggression at 24 months. These pathways principally suggested heterotypic continuity in physical aggression.