Young learners have an innate scientific curiosity and capacity for discovery that can be effectively nurtured through STEM (Science, Technology, Engineering, Mathematics) education that closely aligns with children's everyday experiences. Early childhood educators recognize the critical role of STEM education in cultivating adaptive and transformative skills essential for the twenty first century. This study investigated the effect of a STEM program on increasing children's awareness of sustainability issues. Using pre- and post-interviews, the purpose of the study was to examine the change in children's understanding of the content and skills associated with waste, reduce, reuse, and recycle concepts within the Zero Waste Hierarchy. The results showed a notable improvement in children's understanding of recycling. However, there was a gap in children's understanding of the concepts of 'reduce' and 'reuse'. The research highlighted the importance of integrating sustainability education into STEM programs to improve the understanding of content and skills related to sustainability to contribute to building a sustainable future.