The mediating effect of parenting style on the relationship between first-born children’s temperament and psychological adaptation

Chinese first-born children need to learn how to get along with their siblings after the implementation of the universal two-child policy in 2016. We investigated the relationships between temperament, parenting style, and psychological adjustment among firstborns. The current study employed a questionnaire survey conducted in four regions in China. A total of 524 Chinese two-child families participated in the study; the firstborns were between 3 and 8 years old and their younger siblings were between 1 month and 5 years old. The results indicated that (1) children’s temperament subscales were significantly related to parenting style subscales and psychological adaptation. Moreover, the parenting style subscales were significantly related to psychological adaptation, and (2) authoritarian parenting partially mediated the relationship between approach or withdrawal and psychological adjustment.

www.nature.com/scientificreports/ lack of adjustment (e.g., clinginess), and poor emotional management skills (e.g., crying), affecting their response to the second-born child 18,19 and demonstrating less pro-social behavior 20 . First-born children with difficult temperaments often resist their siblings' birth, and show poor social adaptation and social interaction skills 7 along with difficulty in establishing positive interpersonal relations 12 . 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 14 . 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 21 . 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 3 . Previous studies have found that the activity levels and emotional aspects of temperament impact first-born children's adaptation 13,22 . 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 23 ; those with relatively regular living habits are more likely to adapt well to newborns 24 .
Along with temperamental characteristics, parenting styles, which reflect parental beliefs, attitudes 25 , and behaviors 26 while raising their children 27 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 28 . Firstborns show problematic behavior when their parents make excessive demands 29 . 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 30 and adversely influencing children's personality development and their ability to understand and explore novelty in their surroundings 31 .
Thus, on the one hand, children with difficult temperament are more likely to exhibit problematic behaviors after the birth of their younger siblings 32 . On the other hand, temperament types may affect the problematic behaviors of firstborns through parenting styles. Due to the difficult temperament of the first born children, their parents may be more likely to adopt an authoritarian parenting style without a better choice, which may also lead to more problematic behaviors in firstborns 12,33 . Therefore, it is reasonable to believe that parenting style may mediate the relationship between children's temperaments and problematic behaviors.
While current researches have focused on maternal parenting behaviors such as punishment, excessive control, and overprotection 34 , less attentions have 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 35 . 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 36 .
Based on the DES model and the framework of the Belsky model 32 , Feinberg 37 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). www.nature.com/scientificreports/

Method
Participants. The study was approved by the Research Ethics Committee of the first author's institution.
A total of 600 two-child families were randomly recruited from Shanxi, Shaanxi, Hainan and Shanghai . The questionnaire was completed by the mothers of the children. After removing 76 families whose questionnaires were incomplete, 524 families finally entered the study. There were 261 male and 263 female firstborns ranging from three to eight years old (M = 6.00, SD = 1.62) and their younger siblings (251 male and 273 female), ranging from one month to five years old (M = 3.30, SD = 1.84). The age difference between firstborns and their younger siblings was three years. 70% of families (n = 368) had a combined income of over $10,000, and 60% of parents had a college degree or above (n = 314).
Psychological adaptation. The First-Born Behavior Questionnaire was used to evaluate firstborns' psychological adjustment. It was developed from the Child's Behavior Questionnaire (Mother Assessment) 38 and comprises 18 questions in five subscales 39 . The subscales' Cronbach α varies from 0.70 to 0.82. The higher the score in the First-Born Behavior Questionnaire, the worse the psychological adjustment.
Temperament scale. The Temperament Questionnaire 24,41 comprises 72 items across nine subscales, among which four were used in this study: (1) activity level (e.g., "Active, unable to settle down, and constantly runs, climbs up and down, or twists the body when playing in the amusement park"; Cronbach's α = 0.62); (2) quality of mood (e.g., "Looks significantly happy when playing with other children"; Cronbach's α = 0.61); (3) rhythmicity (e.g., "Defecates regularly every day"; Cronbach's α = 0.65); (4) approach/withdrawal (e.g., "Likes to try new foods"; Cronbach's α = 0.60). Participants respond on a 7-point scale ranging from one (never) to seven (always). A higher score on each dimension represents higher speed and frequency of physical activity, more friendliness, more regularity in eating and living habits, and reduced distance from the new environment.

Discussion
Relationships among temperament, parenting style, and psychological adaptation of first-born children were examined. First, highly active or emotionally intense temperaments were positively associated with psychological maladaptation, which was consistent with some previous findings in Western literature 7,8,12,[14][15][16][17][18][19]21 . We also found that approach/withdrawal predicted psychological adjustment, which suggested that first-born children who willingly approached new environments could adapt to a younger sibling's birth, while those who avoided new environments exhibited maladaptation. This finding is similar to those of previous studies on Chinese only children in kindergarten, whose approach/ withdrawal predicted their psychological and physical changes 42 , and also predicted the teacher-student relationship quality two years later 43 . First-born children who tended to approach new environments are more likely to adapt well to their new siblings. The second-born child's birth did not cause pressure, and they did not need to mobilize their psychological resources to cope, which reduced the degree to which they perceived this stressful event as a potential threat. However, young children generally avoid new environments due to the fear of the changes in the family 44 . This can be explained by Family Stress Theory, which stated that a second-born child's birth is perceived as a life-stressing event for first-born children and their families, presenting as an inevitable psychological threat to each family member 21,34,39 . Therefore, it was normal for first-born children to show a significant increase in behavioral problems and psychological discomfort during the transition period. If first-born children changed their attitudes toward the second-born children, the stress would be reduced, benefiting their adaptation 45,46 .
Second, our results suggested that authoritarian parenting partially mediated the relation between approach or withdrawal and psychological adaptation. In one case, the more a child's temperament leans toward withdrawal, the more likely his parents are to adopt an authoritarian parenting style, which may lead to the worse the child's psychological adaptation. This was consistent with previous results that parenting style was an important factor affecting children's reaction 47 . Parents' warmth or control were key factors regarding children's obedience 48 , and different kind of parents played a different role in preschool children's emotional approach/withdrawal. Another case is, the more a child's temperament leans toward approach, the less likely his parents are to adopt an authoritarian parenting style, which may lead to the better the child's psychological adaptation. And this finding was also consistent with previous studies that children in low-control families were more likely to develop independently 49 , and those with stronger independent abilities would not rely excessively on other people 43 ; hence, they could adapt better.
According to Volling's 36 DES and Feinberg's 37 co-parenting ecological models, children's and family's characteristics have a combined effect on their adaptation. Approach/withdrawal temperament was a contributing factor to authoritarian parenting. The more reluctant the firstborns were in accepting the secondborns during the transition period, the more the parents would be arbitrary and demand their children do things according to their standards, ignoring firstborns' inner feelings, show a lack of patience and enthusiasm, failing to encourage and praise, and require firstborns to obey commands unconditionally. When such conditions prevail, first-born children reject novelty and develop personality traits such as low self-esteem, withdrawal, anxiety, and inhibited adaptability.

Implications and limitations.
China's universal two-child policy significantly affected every family. The birth of the second child often causes some physical and psychological problems compared to that of the first. To raise second-born children, parents use a lot of time, resources, and attention that were originally solely focused on firstborns. Compared to the parents of two or more children, parents of only one child need to pay special attention to a new type of relationship that emerges after the birth of the second child, Parents should focus on first-born children's abnormal behaviors and mental health regularly. Those with a withdrawal temperament often have low self-regulation ability. As parenting style is an adjustment factor, parents should adopt individual and differentiated parenting styles. They should focus on communicating with first-born children, showing them more care and understanding. Some parents adopt an authoritarian parenting style toward firstborn children because of excessive work or parenting pressure, and solve parenting problems in an abrupt and violent manner. To alleviate the pressure of second-child pregnancy, it is recommended that second-child birth subsidies, specific social care and special treatment for second-child mothers, or reproductive assistance in the community to relieve their economic and work pressure should be provided.
This study has several limitations. First, psychological adjustment questionnaires mainly cover behavioral and emotional problems but neglect interpersonal adaptation (e.g., sibling relationships, parent-child relations). Second, All the data were obtained by parental questionnaires and the measurement of parenting styles only addresses mothers' perspective. Future studies may try to collect data from multiple informants (e.g., fathers and grandparents) to deepen the current findings.Third, parents' sibling status and their own lack of experience in managing negative emotions related to their sibling's birth were not included in the study. It should be an important measure in futures studies on the subject.

Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.