siblings

The U.S. National Institutes of Health has dedicated its considerable resources to investigating one of the more infuriating aspects of growing up with siblings: the nagging sensation that your sibling gets preferential treatment. The takeaway from a new study suggests that your siblings are justified. Mom does treat each of her multiple children differently — but it’s probably not because you were born first (or second)

Motivated by a gap in the literature when it comes to the social and emotional dynamics of moms and siblings, a team of four experts in child development at the NIH, headed by Marc H. Bornstein, Ph.D., the recently retired head of the NIH’s Child and Family Research division, applied some scientific rigor to those anecdotal feelings of inequity. Their research, published in Social Development, shows that there are significant differences in how mom interacts with each of her two children, but they’re not differences in preference.

“There was no observable preference for the first or second child,” Diane Putnick, a study co-author a developmental psychologist at the NIH tells Inverse. “Instead what we observed was that each relationship seemed unique.”

Putnick quantified these unique interactions by observing two hours of interactions between 55 mothers and their first-born children when the kids were 20 months old. With those tapes in the archives, she then returned years later, when the second siblings were born and reached 20 months of age. What emerged from this was a scientific version of your most embarrassing childhood home videos, played and replayed by a team of cognition experts.

They found that mothers were consistent in their attitudes about parenting: For instance, they tended to have the same values even after having a second kid, which Putnick calls “socioemotional parenting cognition.” But when it came to putting those values into practice, things usually tended to vary by child, which she calls “socioemotional parenting practices.”

So, while moms tried to apply the same parenting rationale to both their kids, it didn’t really work out in application. Mothers engaged in 15 percent more play with older children, and younger siblings received roughly four percent more praise and 9 percent more physical affection. Putnick, however, is careful to highlight that these differences are far from universal.

siblings social play
The team did notice some small differences in praise, social play and physical affection, but nothing that they thought was significant to establish a trend. 

Interestingly, these results show that it isn’t actually birth order that cause differences in a mother’s treatment between her children. Instead, these researchers believe that it really comes down to the personality of each child, which, to make this even more circuitous, is affected by birth order. This study shows that first-born children are more sociable than second-born children, which Putnick suggests might be due to “years of undivided attention before a sibling is born.”

Ultimately, it might be differences in personality due to birth order that lead a mom to adapt different parenting styles for each child, says Putnick, and these in turn might explain why some moms “engaged in more play” with older siblings than younger ones. “I think that maternal practices differ between their two siblings because individual children have unique characteristics,” she explains. So it seems that parents who treat their kids the same might be fighting an uphill battle: not against birth order, but against the personalities of their children.

“As much as parents might try to treat sibling children similarly,” she concludes, “their children’s individual needs may dictate different parenting.”