Physical aggression has its origin very early in development, but no studies to date have examined physical aggression trajectories starting before the age of 1.5 years. This study examined whether cognition plays a role in the development of physical aggression from infancy onward. In a sample of 182 mother-child dyads (94 boys; 88 girls), child physical aggression was assessed by maternal report using the Physical Aggression Scale for Early Childhood at 12, 20, and 30 months. Children performed cognitive tasks measuring inhibitory control and attention, and mothers rated children's vocabulary at 12 and 30 months. Results showed that differential development of physical aggression already starts at 12 months of age: low-stable, low-increasing, moderate-decreasing and high-stable trajectory groups were identified. Inhibitory control, attention and vocabulary at 12 months and development of these abilities from 12 to 30 months were selectively related to the likelihood of following the low-increasing and moderate-decreasing trajectories compared to the low-stable physical aggression trajectory. This study is the first to show that specific aspects of cognition and cognitive development are related to differential physical aggression development from infancy onward.

Prenatal risk and a lack of inhibitory control have consistently been related to the development of physical aggression in older children. This study examined whether inhibitory control mediated the relation between prenatal risk and aggression in infants and toddlers. The role of gender in this mediation model was also examined. The sample consisted of 161 mother–child dyads (83 boys). A prenatal cumulative risk score was created from a number of well‐established risk factors including maternal psychopathology, substance use, and social and socioeconomic disadvantages. At 12 months, children performed an inhibitory control task. Physical aggression was assessed through maternal reports at 12 and 20 months of age. Results showed that higher prenatal risk was associated with more physical aggression. Inhibitory control mediated this association at both 12 and 20 months: higher prenatal risk was related to lower inhibitory control, which in turn led to higher aggression. At 20 months, gender moderated the mediation effect: the mediating role of inhibitory control was only found for girls. These results suggest that even before 2 years of age, inhibitory control is an important construct involved in the relation between prenatal risk and physical aggression.

Prenatal risk, temperamental negative affect, and specific cognitive abilities have all individually been identified as predictors of behavior problems during early childhood, but less is known about their interplay in relation to aggression during toddlerhood. This study examined the main and interaction effects of prenatal risk, negative affect, inhibitory control, attention, and vocabulary in the prediction of aggression in 150 children (75 boys). During pregnancy, a cumulative risk index was calculated based on the presence of 10 well-established maternal risk factors, such as prenatal substance use, maternal psychiatric disorder, and financial problems. Negative affect was measured at 6 and 20 months using maternal report. Child cognition was examined at 30 months using laboratory tasks for inhibitory control and attention, and a questionnaire was administered to assess vocabulary. In addition, mothers reported on their children's aggressive behavior at 30 months. Higher prenatal risk and negative affect at 20 months and, to a lesser extent, at 6 months were related to more aggression at 30 months. Poorer inhibitory control and, to a lesser extent, vocabulary at 30 months also predicted higher levels of aggressive behavior. Two-way interaction effects were found for cumulative risk and inhibitory control, negative affect (at 20 months) and inhibitory control, and negative affect (at 6 months) and vocabulary: aggressive behavior was most pronounced when combinations of high prenatal risk, high negative affect, and poor cognition were present. These results suggest that the impact of prenatal risk and child temperament depends in part on child's cognitive development during toddlerhood.

Parental beliefs, parenting behavior, and precursors of theory of mind have been related uniquely to each other and to early aggression, but have not yet been studied simultaneously. The present study combined these risk factors in the prediction of aggression during toddlerhood using a sample of 152 mother–child dyads. At 20 months, mothers' parental beliefs (parental self‐efficacy and perceived parental impact) were examined with the Parental Cognitions and Conduct Toward the Infant Scale. Maternal parenting behavior (sensitivity, intrusiveness, and successful positive engagement) was observed during free play and teaching tasks, and children's precursors of theory of mind were assessed using a visual perspectives task and an imitation task. At 30 months, child aggression was examined using the Child Behavior Checklist. A regression analysis indicated that lower parental self‐efficacy and lower imitation skills predicted more aggressive behavior. When estimating the indirect effects using bootstrapping, a final model was found indicating that lower perceived parental impact was related to less successful positive engagement, which, in turn, was associated with children's poorer imitation abilities which predicted more aggressive behavior. It can be concluded that aggression during toddlerhood is predicted significantly by interrelated parental beliefs, parenting behavior, and children's early social cognitive abilities.