On January 1, 2016, China ended the one-child policy that had been implemented for more than 30 years, by allowing couples to have two children. Five years later, in 2021, China further relaxed this limitation and now permits three children per couple. Most preschoolers also changed from single children to first-born children. For the latter, who are accustomed to being the only child, the second or third child’s arrival causes adjustment difficulties. Negative news reports about the first-born child in two- or three-child families are also increasing[1]. First-born children’s psychological adaptation to siblings has received significant attention in Chinese society and academic circles. Psychological adaptation is the process by which individuals adjust to changes in the external environment to ensure that their covert dispositions and overt behaviors are more consistent with the requirements of environmental changes and their personal development. Hence, through this process, the subject and the environment achieve a new balance[2]. In this study, psychological adaptation during the transitional period is mainly manifested in emotion and behavior.
Changes in family relationships and environment after the birth of a second child may result in diverse reactions in first-born children. There are individual differences in whether firstborns experience distress after the birth of their siblings[3]. Some children experience distress and exhibit destructive behaviors[4] such as jealousy, grumpiness, and aggressive tendencies. However, some react positively[5, 6]. They might hug, offer to help, and even kiss the newborns. Most children’s reactions tend to be a combination of these two.
Children’s temperament is an important individual difference[7]. Firstborns with difficult temperaments (highly active and emotionally intense) are reluctant to accept their younger siblings[8–11]. Children of different temperaments respond differently. For instance, those with difficult temperaments who protest when their mothers look after their 14-month-old younger siblings, often feel negative emotions such as anger[5, 12]. They could exhibit a propensity for emotional disorders or maladaptive problems[13–15], and often show negative emotions (e.g., anger), lack of adjustment (e.g., clinginess), and poor emotional management skills (e.g., crying), affecting their response to the second-born child[16, 17] and demonstrating less pro-social behavior[18]. First-born children with difficult temperaments often resist their siblings’ birth, and show poor social adaptation and social interaction skills[5] along with difficulty in establishing positive interpersonal relations[10]. For example, previous studies have suggested that first-born children with difficult temperaments demonstrate more social deviations and sleep problems during the transition period, and are less willing to take care of their siblings[12]. Dunn found that those with more negative emotions had more social withdrawal, insecure attachment, and sleeplessness, and were unwilling to help after the second child’s birth[19]. A study suggested that the second child’s arrival and the change in the first child’s identity may prompt a shift in the first child’s temperament type to a difficult one[1].
Previous studies have found that the activity levels and emotional aspects of temperament impact first-born children’s adaptation[11, 20]. How do approach/withdrawal and rhythmicity, which have a relatively stable temperament dimension in infants and young children, affect firstborns’ psychological adjustment? Approach or withdrawal refers to children tending to approach or avoid the new environment, and rhythmicity reflects the regularity of their diet and daily life. Research suggests that children who enjoy the new environment tend to be more socially competent[21]; those with relatively regular living habits are more likely to adapt well to newborns[22].
Along with temperamental characteristics, parenting styles, which reflect parental beliefs, attitudes[23], and behaviors[24] while raising their children[25] are important during the change in firstborns’ identity. An appropriate parenting style can reasonably coordinate sibling relationships and promote a smooth transition. There is a strong connection between parenting styles and children’s problematic behaviors[26]. Firstborns show problematic behavior when their parents make excessive demands[27]. Tan et al. found that parents with greater pressure were more inclined to choose authoritarian parenting styles, leading to an increase in covert and overt behavioral difficulties[28] and adversely influencing children’s personality development and their ability to understand and explore novelty in their surroundings[29].
Children with difficult temperaments exhibit problematic behaviors after the birth of siblings. However, if they are actively supported by parents and family members, several potential issues are mitigated[30]. Kolak reported that when parents adopted authoritarian parenting styles, firstborns with difficult temperaments exhibited problematic behavior[10] that increased with the increase in maternal corporal punishment[31]. Another study found that if parents choose a parenting style appropriate to their child's temperament, problematic first-born behavior can be reduced. When a democratic parenting style is adopted, first-born children with difficult temperaments are willing to take care of their siblings[11].
Hence, the mediating role of parental behavior between child temperament and problematic behaviors is confirmed. While current research has focused on maternal parenting behaviors such as punishment, excessive control, and overprotection[32], less attention has been paid to the parenting style of non-one-child families and other aspects of firstborns’ psychological adjustment. Among first-born children, emotionality and activity receive more attention, while approach or withdrawal and rhythmic temperament receive less focus. Specifically, there are few studies on first-born children in mainland China. Therefore, this study explored the relationship among parenting style and firstborns’ temperament and adjustment adaptation in China.
Temperament, which plays a unique role in children's development independent of the environment, interacts with environmental factors to jointly affect childhood development and adaptation[33]. Volling proposed a developmental ecological systems (DES) model to examine the change in family and children’s functioning during the transition to siblinghood. In the DES model, children are placed in the ecological environment and the system indicates that the internal and external systems of the family are important for children’s adaptation. Children grow up in a dynamic and constantly changing environment. The DES model analyzes their environment across the following levels: (a) parents’ psychological characteristics, e.g., their well-being and personality characteristics; (b) children’s characteristics, e.g., temperament; (c) family environment (microsystem); (d) the larger social environment wherein the family is located. Each system influences children’s development and adaptation through their interaction[34].
Based on the DES model and the framework of the Belsky model[30], Feinberg[35] proposed the co-parenting ecological systems, which discussed the relationship between the family system and children's developmental adaptation regarding three aspects: individual, family, and environment. Children's characteristics affect their adaptation directly through the mediating effect of co-parenting.
Based on these previously discussed studies and theories, we hypothesize that first-born children’s adjustment adaptation will be directly affected by their temperament and parental style, and temperament will also affect first-born children's adaptation through the parenting style (see Fig. 1).
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