Often, when people talk about child abuse, they repeat the "party line" that most abuse happens in the home. Sometimes they say "in families." What Broken Homes and Battered Children showed was that families where two natural parents are living with their own children are comparatively safe environments and that marriage is a protective factor in and of itself. the most dangerous environment in terms of incidence of child abuse was found to be homes where a single parent was living with a partner who was not the natural parent of the child(ren).
Recently the US Department of Health and Human Services received the Fourth National Incidence Study of Child Abuse and Neglect. One of the members of the Research Advisory Group for this study was Dr Patrick Fagan, Director of the Marriage and Religion Research Institute at the Family Research Council. He successfully pressed for data on family structure to be incorporated in the study. As a result, a significant section of the report deals with (Section 5.3 Differences in the Incidence of Maltreatment Related to Family Structure and Living Arrangement - pp 5-18 to 5-39)
One of the summary statements in this section of the report reads:
All maltreatment. Children living with two married biological parents had the lowest rate of overall Harm Standard maltreatment, at 6.8 per 1,000 children. This rate differs significantly from the rates for all other family structure and living arrangement circumstances. Children living with one parent who had an unmarried partner in the household had the highest incidence of Harm Standard maltreatment (57.2 per 1,000). Their rate is more than 8 times greater than the rate for children living with two married biological parents.Here is the chart:
In short, if people tell you that most abuse occurs "in families", you can point out that in the family as in married parents who care for their own children, the risk has been shown to be much lower than in other kinds of living arrangement.