Parents certainly aren't absent from sibling dynamics, either, and children are acutely aware of preferential treatment.
"Siblings report that what bothers them is when parents play favorites, especially in an ongoing fashion," said Katherine J. Conger, an associate professor of family research at the University of California, Davis, who co-edited and published research in the recent journal volume on siblings.
"Social comparison can also be hurtful if parents are always holding up Suzy as the smart one, and why can't you be more like your sister?" Conger said.
But teaching parents and children how to foster positive social interactions at home can promote healthy sibling relationships for life.
Working with children as young as four years old on conflict management, emotionality and perspective, Kramer has witnessed promising changes in sibling relationships.
Conger agrees with Kramer's findings.
"Siblings can learn to play cooperatively and even unlearn conflicting patterns of behavior from a very young age," Conger said. "But part of it is re-training parents so that they also promote positive social interactions and don't just respond to squabbles with the age-old 'just leave your sister alone!'"