This paper draws on a multi-phase project that sought to understand and increase young children's engagement with Science, Technology, Engineering and Mathematics (STEM) objects. The paper presents findings from one aspect of this project that involved using storytelling to support young children's agency with STEM objects in a UK science museum. The qualitative research involved observing and interviewing 25 children aged 4-7 years in family and school groups. The findings demonstrate the importance of acknowledging and promoting young children's agency in museum settings. They suggest that providing children with opportunities to exercise agency by them taking control and activating their prior knowledge and interests during museum visits increases their engagement, enjoyment, and confidence. The study also highlights the important role that adults, including parents, teachers, and museum staff, play in facilitating children's agency and increasing their engagement with museum objects and spaces.