Are older siblings in a family more likely to be physically abused than their younger siblings? Does the number of children in the family affect the likelihood of abuse?

We know a great deal about factors that contribute to child abuse—like poverty, or drug abuse by a parent—things that increase the risk of violence expressed toward children. I want to focus instead on why abusive parents often direct aggression toward one child but not others within the same family. Abuse is rarely distributed equally—it’s often just one child who bears the brunt of a physically abusive parent. Which child tends to be singled out, and why?

To make sense of this, we should start by comparing child abuse to any other type of crime. In general, the perpetrators of a crime try to conceal their actions from witnesses, so that other people serve as a kind of surveillance that discourages the criminal actions. This means that the more children there are in a household, the more difficult it will be to keep the abuse a secret. The presence of other children should be an even stronger deterrent if they’re old enough to understand what’s going on and if they’re capable of intervening. So, for example, the youngest sibling will tend to be more protected from mistreatment than the eldest child ever was, growing up in the same home without older siblings.

This “surveillance” theory of abuse was tested in a study that looked at households where there was serious physical abuse committed against at least one of the children, as reported to a local child protective agency. Because this study was interested in siblings, they only focused on abusive households that had two or more children, to see which children were at greater risk of maltreatment.

Consistent with the surveillance theory, the risk of victimization was lower when a child had more siblings overall, and lower still when these were older siblings. A child’s risk decreased even further when there was a large age difference between themselves and their older siblings, and when the older siblings were brothers. Thus, having more mature and perhaps more powerful siblings probably deterred abuse against the later-born children. Even having younger siblings may be enough to discourage abuse too, as long as they’re capable of reporting what they see.

Unfortunately, the flip side is that the oldest child (or an only child) doesn’t have the benefit of this extra surveillance in these toxic homes. In these cases, the presence of other family members will likely be all the more critical.

None of this is meant as an argument to have additional children, nor to foster paranoia about potential abuse. Rather, it shows us how birth order and the social composition of a family can have enormous consequences.

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