There was no evidence to support the popular assumption that peer and sibling violence had less mental health effects on younger than older children. The violent incidents between younger children and their peers and siblings were no less serious than the violent incidents that involved older youth in terms of the severity of injuries. Neither were their differences in the trauma symptoms evidenced in the two age groups (anger, depression, and anxiety). For younger children, however, increased trauma symptoms only appeared for victims of chronic sibling violence (five or more violent episodes in a year), not for children experiencing only infrequent episodes of violence. Older youth showed some weakly increased trauma symptoms at low levels of sibling victimization and none at chronic levels. This suggests that younger children may be more resilient in coping with a modest amount of sibling aggression. The study obtained reports on past year's violent victimization and childhood mental health symptoms in a national probability telephone sample of 2,030 children and youth ages 2 through 17. The experiences of violence for 10- to 17-year-olds were obtained through self-reports, and those of the 2- to 9 year-olds were obtained from caregivers. The survey was conducted between December 2002 and February 2003. Exposure to violent victimization was determined with the Juvenile Victimization Questionnaire. The Trauma Symptoms Checklist for Children was used to identify trauma symptoms for 10- to 17-year-olds, and the Trauma Symptom Checklist for Young Children was used in the caregiver interviews for the younger group. 3 tables, 2 figures, and 55 references