Girls are less likely to be physically abused by a parent. Boys are more likely to be abused and most likely by the mother. (Gurian, Michael. The Wonder of Boys. NY: Jeremy P. Tarcher/Putnam, 1996, pp 94-96)
In adulthood, 25%-35% of children who were abused, abuse their own children physically or sexually. About 40% of children, who witnessed either parent striking the other, will become spouse beaters. (Diamond, Marian, PhD, and Janet Hopson. Magic Trees of the Mind. NY: A Dutton Book 1998, pp 130-132)
Maltreatment can have enduring effects on a child's developing brain, diminishing growth and reducing activity in key areas. (Teicher, Martin H. Scars That Won't Heal: The Neurobiology of Child Abuse. Article.)
Refer to Trauma and the Brain for additional information.