Adjustment to the birth of a sibling and issues of sibling conflict are among the most common concerns expressed by parents of young children (Brody & Stoneman, 1987). Eighty percent of children live with at least one sibling (Stillwell & Dunn, 1985), and it is within the often intense and close relationships between brothers and sisters that children learn important social and cognitive skills. Many argue that sibling relationships are a major influence on the development of individual differences in antisocial and prosocial behavior, as well as aspects of personality, intelligence, and achievement (Smith, 1993; Stillwell & Dunn, 1985). Research in this area has shown that various family and child factors influence children's adjustment to a new sibling, as well as the quality of the relationship that develops between children and their brothers and sisters. Siblings influence each other's development both directly (by modeling or differentially reinforcing appropriate or inappropriate behaviors) and indirectly (by causing stress for parents, which in turn affects parenting skills). Interactions between two siblings increase rapidly when the younger one is between 3 and 4 years of age, but remain fairly consistent in frequency after that time (Dunn, Creps, & Brown, 1996). Moreover, anger, distress, and conflict decrease as the younger sibling reaches school age (Dunn et al., 1996). This most likely reflects the children's increased involvement with friends at school and with other activities outside the home.
Sibling relationships are quite different from peer relationships, in that they are “vertical” (the participants have unequal status) rather than “horizontal” (the participants have equal status) (Brody & Stoneman, 1983; Hartup, 1989). Research has shown that there is little relationship between the behavior of children with their siblings and with peers (Berndt & Bulleit, 1985). Incidents involving conflict, for example, occur with similar frequency between siblings and between peers, but those involving physical or verbal aggression are much more frequent between siblings (Dunn & Munn, 1985, 1986a; Shantz, 1987). Moreover, siblings are less likely to use compromise or reconciliation in the resolution of conflict than are peers (Killen, 1991; Phinney, 1985). This chapter first reviews the research on how children adjust to the birth of a new sibling, and presents suggestions for intervention in/prevention of adjustment problems. Next, issues of sibling conflict are discussed; the critical assessment issues for such conflict are outlined; and suggestions for treatment of sibling rivalry are presented.