Theory of mind (ToM) adalah kemampuan individu memahami keadaan mental diri dan orang lain yang berkaitan dengan tingkah laku prososial anak. Penelitian mengenai ToM banyak dihubungkan dengan kemampuan bahasa sebab bahasa berperan sebagai kognisi sosial. Penelitian lainnya melihat faktor saudara kandung juga diduga dapat memengaruhi ToM anak. Saudara kandung dapat menjadi sosok sebaya dalam berinteraksi, memahami intensitas emosi satu sama lain, dan membantu dalam pemahaman sosial-kognitif. Penelitian sebelumnya telah mengaitkan bahasa dengan ToM (Bigelow et al., 2021) dan mengaitkan saudara kandung dengan ToM (Leblanc et al., 2017; Zhang et al., 2021; Hou et al., 2022), tetapi hasil penelitian bervariasi. Penelitian-penelitian tersebut menduga saudara kandung dapat menjadi teman berinteraksi sosial anak dan dapat menguatkan atau justru melemahkan kemampuan bahasa anak yang nantinya memengaruhi ToM-nya. Penelitian ini pun dilakukan atas dasar tersebut. Penelitian ini merupakan penelitian korelatif dengan pengujian analisis regresi linear sederhana untuk melihat hubungan antara kemampuan bahasa dan ToM dan simple moderation berbasis regresi dengan bootstrapping untuk melihat peran saudara kandung terhadap hubungan kemampuan bahasa dan ToM anak. Partisipan penelitian merupakan 117 anak berusia 4–7 tahun di Jabodetabek yang diperoleh melalui convenience sampling. Hasil penelitian menunjukkan bahwa kehadiran saudara kandung diketahui memoderasi (menguatkan pengaruh) kemampuan bahasa terhadap ToM secara signifikan (b = 0,19, SE = 0,07, t = 2,45, p = 0,01, 95% confidence interval [CI] [0,03, 0,35]). Penelitian lebih lanjut diperlukan untuk meninjau interaksi ketiga variabel ini dalam partisipan dari disadvantage family, melihat secara spesifik aspek saudara kandung, serta melihat bentuk kualitas interaksi saudara kandung dengan anak.

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Theory of mind (ToM) is the ability of an individual to understand the mental states of oneself and others, which is related to children's prosocial behavior. Research on ToM was often linked to language abilities, as language played a role in social cognition. Other studies explored the impact of sibling factors on children's ToM. Siblings could serve as peers in interaction, understanding each other's emotional intensity, and contributing to social-cognitive understanding. Previous research had associated language with ToM (Bigelow et al., 2021) and linked siblings to ToM (Leblanc et al., 2017; Zhang et al., 2021; Hou et al., 2022), but research findings varied. These studies suggested that siblings could become social interaction companions for children and might either strengthen or weaken a child's language abilities, subsequently influencing their ToM. This research was conducted on this basis. This study was correlational, employing simple linear regression analysis to examine the relationship between language ability and ToM. Additionally, simple regression-based moderation with bootstrapping was performed to observe the role of siblings in the relationship between language ability and children's ToM. The research participants were 117 children aged 4–7 years in Jabodetabek obtained through convenience sampling. The results indicated that the presence of siblings significantly moderated (strengthened the influence of) language ability on ToM (b = 0,19, SE = 0,07, t = 2,45, p = 0,01, 95% confidence interval [CI] [0,03, 0,35]). Further research was needed to examine the interaction of these three variables in participants from disadvantaged families, specifically looking at aspects of siblings, and assessing the quality of sibling interactions with the child.