That younger siblings are most likely to experience bullying within a family, and the eldest is most likely to do the bullying may not come as a surprise to those who grew up in large broods.
The bigger the family, the more likely there will be bullying within sibling ranks, a UK study suggests.
Within larger families, the babies are most likely to be bullied while the perpetrators are probably boys and probably the oldest kids in the house, researchers found. But among kids who were involved in bullying at all, the majority were both bully and victim at different times.
Identifying the factors that influence a child's risk for being on either side of the bullying dynamic could help in formulating ways to avert this behaviour, the authors write in Developmental Psychology.
"Most importantly, sibling bullying was not related to whether this was a two- or single-parent household, income or social class - it occurs in poor and rich families alike," said study co-author Dieter Wolke, a psychology researcher at the University of Warwick in Coventry.
"Siblings fight about the resources that are available whether attention or food in poorer households or the new smartphone in rich families," Wolke said by email. "It is about the relative dominance within the family!"
Roughly 85 per cent of children grow up with at least one other child in the family, Wolke's team notes. While these are some of the longest-lasting close relationships for many people, they can also be characterized by escalating conflicts that lead to lasting physical and mental health problems.
For the current study, researchers analysed data on 6,838 British children born in 1991 and 1992, as well as their mothers.
When children were 5 years old, their mothers reported how often kids were victims or perpetrators of bullying in the household. Then, when kids reached age 12, they reported their own experiences with bullying in the previous six months as well as the age when they first were involved in this behaviour as a victim or perpetrator.
Researchers defined sibling bullying as psychological abuse like saying nasty or hurtful things, physical abuse like hitting or kicking or pushing, or emotional abuse like telling lies or spreading hurtful rumours. They put kids in four categories based on their experiences: victims, bullies, bully-victims who experienced this as both targets and perpetrators, and those who didn't have any involvement with these behaviours at all.
They also looked at individual family, parent and child characteristics like total number of kids at home, mother's marital status, family socioeconomic background, and exposure to domestic violence or child abuse.
Overall, 28 per cent of the kids in the study were involved in bullying as victims, perpetrators, or both.
Psychological abuse was most common, affecting 41 per cent of victims and practiced by 34 per cent of perpetrators.
A total of about 11 per cent of the kids were both bullies and victims, the study found. About 10 per cent reported being only victims and 7 per cent were only perpetrators.
"There are many ways bullying is carried out in families," said Bonnie Leadbeater, a psychology researcher at the University of Victoria in Canada.
"Sometimes it is hidden by the victim who fears getting the bully into trouble," Leadbeater, who wasn't involved in the study, said by email. "Sometimes there is an 'odd man out' kind of family dynamic where one child is teased and targeted by the others who think they are being funny or are deliberately being punitive in a misguided effort to change what they see as a problem (e.g. the child seems odd, weak, or cries easily)."
That doesn't mean parents are powerless to change these dynamics.
"One way that parents can prevent bullying and victimization is by coaching children through strategies about how to handle challenging situations (like disagreements with siblings)," said Stevie Grassetti, a psychologist at West Chester University in Pennsylvania.
"Parents should talk to their children about their values and expectations and help guide children into interacting with siblings in prosocial ways. For children who are bystanders to bullying between siblings, parents should reinforce intervening on behalf of victims," Grassetti, who wasn't involved in the study, said by email.