Perilaku agresif kakak usia prasekolah kepada adik bayi baru lahir dapat dikurangi dengan meningkatkan perilaku prososial (Carlo dkk. 2014, dalam Beier dkk. 2019). Ibu berperan penting dalam perkembangan perilaku prososial anak dengan memberikan pengasuhan yang hangat dan kualitas hubungan yang baik (secure attachment) (Eisenberg, Spinrad, & Knafo-Noam, 2015). Partisipan penelitian adalah ibu yang memiliki 2 anak, anak pertama usia prasekolah, anak kedua berusia bayi. Attachment diukur menggunakan PCRI (Marcus, 2001 dalam Hapsari, 2009). PRF diukur menggunakan PRFQ (Luyten dkk. 2017). Perilaku prososial anak usia prasekolah diukur menggunakan alat ukur perilaku prososial anak prasekolah kepada adik bayi yang dibuat oleh Dwitya (2012). Hasilnya menunjukkan Attachment tidak berperan secara signifikan menjadi mediator antara Parental Reflective Functioning dan perilaku prososial kakak kepada adik bayi.

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Aggressive behavior of firstborn preschooler toward newborn sibling can be reduced by increasing prosocial behavior (Carlo dkk. 2014, dalam Beier dkk. 2019). Mothers play an important role in the development of childrens prosocial behavior by providing warmth parenting and good quality relationships (secure attachment) (Eisenberg, Spinrad, & Knafo-Noam, 2015). The research participants were mothers who had 2 children, the firstborn was preschoolers, the second child was a baby. Attachments were measured using PCRI (Marcus, 2001 in Hapsari, 2009). PRF is measured using the PRFQ (Luyten et al. 2017). Prosocial behavior of preschoolers was measured using preschool children's prosocial behavior measurement tools for younger siblings made by Dwitya (2012). The results study shows that attachment did not play a significant role as a mediator between Parental Reflective Functioning and firstborn prosocial behavior toward newborn baby.