Nowadays, some people prefer to have an only child because of the cost of raising children. From the hypothesis, the number of children influences the actions of children who behave in various situations. More precisely, developing, shaping; and affecting selfconfidence, which is different and causes different mindsets in children, depends on the number of children. A person's mindset is a collection of ideas that influence how they perceive themselves, which can divide into two categories: a fixed mindset (where both abilities and skills are innate and cannot be improved) and a growth mindset (where both abilities and skills can be developed via education, experience, and effort). This study aims to identify the correlation between the number of children and Dweck's Mindset Theory. Therefore a 12-item online questionnaire with 12 closed-ended questions was created using a 5-Likert scale to test the hypothesis that children with siblings lead higher self-confidence than the only child. A total of 100 voluntary responses were received. The analysis supported the theoretical framework that there was a moderate positive correlation between the child with siblings and a growth mindset (r=4.23). On the contrary, The correlation between a single child and a growth mindset (r=4.13) was lower than the previous one.Moreover, this research also showed a moderate positive correlation between single children and a fixed mindset (r=2.58), which was higher than the correlation between the child with siblings and a fixed mindset (r=2.22).From this research, There is a responsibility that children with siblings influence the development of individual growth mindsets. Therefore parents and teachers need to enhance their children's skills and abilities through learning, experience, and effort to develop a growth mindset and build selfconfidence in children. In conclusion, a child with siblings is more likely to construct a growth mindset promoting self-confidence.

Keywords : Growth mindset, fixed mindset, a child with siblings, single child, self-confident, sibling relationship, sociability