Sibling rivalry is a predictable, normal, and healthy response to the birth of a new brother or sister. In most families, it demonstrates that the older child is appropriately attached to the parents and is responsive to a perceived threat to the parent-child relationship. It is a normal response to having your place as the baby of the family usurped. In this context, the emergence of behaviour that reflects sibling rivalry should be viewed positively. Ambivalence towards the baby, as evidenced by an ongoing shift between positive and negative behaviour, is to be expected. Indeed, its absence may be worrisome. Sibling rivalry is not a disease but a manifestation of psychological health.
Aggressive behaviour is directed most commonly towardss the mother, but it may also be directed towardss the baby, father, playmates, self, or toys. Aggressive behaviour most often occurs when the older sibling is a toddler. Increases in this behaviour will probably occur when the new baby becomes more socially engaging at 4 to 5 months of age and again when he becomes mobile during the last half of the first year. Open hostility may be reduced to more subtle behaviour directed at the infant, such as pulling the pacifier out of the baby's mouth or taking a toy away.
Naughtiness, or doing things contrary to family rules, occurs frequently at times when the mother is busy with the baby. This strategy serves to both increase tension in the household and verify the continuing power of the toddler to alter the behaviour of those around her. A careful history of when such behaviour occurs may highlight to the family for the first time that it is not “random,” but dependent on a particular situation.
Some children are overly compliant with or overly solicitous of the infant. Perhaps the child fears being totally replaced if she misbehaves, so the child becomes “extra good” to ensure her place in the family. Then again, she may be so frightened of her own aggressive and angry feelings that she holds them tightly in check. This may become a costly strategy and may evolve into an actively aggressive pattern or an irritable, depressed mood.
Regressive and dependent behaviour is usually seen in the form of clinging and demanding. Other possible types of regressive behaviour include sleep disturbances, stuttering, thumb sucking, bedwetting, eating refusals or demands, and baby talk. These responses serve to see whether one can get the same attention and care as the infant. They are also the expected response to any stress or demand for adjustment.
Behavioural manifestations of sibling rivalry reflect a child's limited and primitive response to change in the family structure, including her own position. They generally decrease, but may not entirely disappear, during the year after the new sibling's birth. There may be periods of readjustment as the infant's abilities change. Over this period, the older child becomes confident of a new place in the family, with its status and privileges. Additionally, the older sibling usually develops a separate relationship with the younger child as the latter becomes more fun, responsive, and interactive. Young babies aren't much fun and are usually quite a disappointment to a child initially.
The arrival of a younger sibling can evoke positive behavioural changes as well as negative ones, even in the early get-acquainted period. Dunn and Kendrick report gains in the older child's independence and mastery, particularly with regard to self-help skills (e.g., dressing and feeding). The child may gain new skills and a growing sense of competency through participation in “her” baby's care. She may be able to reflect on her own growth and development as she sees the baby's emerging capabilities. The older sibling may try out new ways of dealing with the little stranger, such as initiating and maintaining interactions in which she bears the burden of greater understanding. She will learn to laugh at the antics of the baby and grow in confidence as she learns to make the infant laugh, play games, and imitate. This is an opportunity for growth if such behaviour is understood and supported.
Here are a number of important limitations in the extant empirical literature on sibling relationships and sibling rivalry. First, the vast majority of research has been conducted on Caucasian, middle-class, Western (British, Canadian, US) intact families. Unfortunately, we know little about the development of sibling relationships in other cultures or demographic groups. The nature of sibling relationships may possibly differ in more collectivistic cultures (e.g., Latin America) vs. the less collectivistic cultures of the industrialised West. Nor do we know much about how sibling relationships may vary within minority ethnic or linguistic populations in the West, rural or urban populations, etc. Only recently have researchers examined the quality of sibling relationships between step- and half-siblings in nontraditional families. Second, researchers have not addressed the nature of sibling relationships in families with more than two children; thus, there is no empirical evidence on the dynamics of families with three or more children.
For example, the kinds of interactions that might exist between first- and thirdborn or second- and thirdborn siblings remain an open question. Third, in many studies, the age gap between the children is confounded with the age of one of the siblings; thus, we know little about the effects of this variable on the quality and types of sibling interaction. Fourth, although there is a small body of literature on the sibling relationships of children with a physical or intellectual disability, the impact of this experience on family and sibling functioning is a neglected area of research. Most studies rely on parental reports or employ questionnaire or interview methods, and there are few naturalistic observational studies examining sibling interactions in these special populations.