Physical aggression in children is a major public health issue. This study examined the trajectories of physical aggression in early childhood and identified predictors of high levels of aggression. A sample of 572 families with a 5-month-old infant was followed, with assessments of physical aggression frequency obtained from mothers at 17, 30, and 42 months. Using a semiparametric mixture model, three distinct trajectories of physical aggression were identified: low aggression (28%), moderate rising aggression (58%), and high rising aggression (14%). Predictors of high aggression included having young siblings, maternal antisocial behavior before high school, early childbearing, low family income, and maternal smoking during pregnancy. At 5 months, coercive parenting and family dysfunction were significant predictors. The study highlights that children who display high aggression early are at higher risk of serious violent behavior later. Results suggest that early intervention targeting these risk factors could prevent future aggression. The study also found that family dysfunction and coercive parenting at 5 months were strong predictors of high aggression. The findings emphasize the importance of early identification and intervention to reduce the risk of violent behavior in adolescence and adulthood. The study underscores the need for preventive programs that address these risk factors, particularly in families with a history of antisocial behavior, early childbearing, and low income. The results indicate that early intervention is critical in helping children learn to regulate physical aggression before entering primary school.Physical aggression in children is a major public health issue. This study examined the trajectories of physical aggression in early childhood and identified predictors of high levels of aggression. A sample of 572 families with a 5-month-old infant was followed, with assessments of physical aggression frequency obtained from mothers at 17, 30, and 42 months. Using a semiparametric mixture model, three distinct trajectories of physical aggression were identified: low aggression (28%), moderate rising aggression (58%), and high rising aggression (14%). Predictors of high aggression included having young siblings, maternal antisocial behavior before high school, early childbearing, low family income, and maternal smoking during pregnancy. At 5 months, coercive parenting and family dysfunction were significant predictors. The study highlights that children who display high aggression early are at higher risk of serious violent behavior later. Results suggest that early intervention targeting these risk factors could prevent future aggression. The study also found that family dysfunction and coercive parenting at 5 months were strong predictors of high aggression. The findings emphasize the importance of early identification and intervention to reduce the risk of violent behavior in adolescence and adulthood. The study underscores the need for preventive programs that address these risk factors, particularly in families with a history of antisocial behavior, early childbearing, and low income. The results indicate that early intervention is critical in helping children learn to regulate physical aggression before entering primary school.