Children as young as 6 months old are captivated by natural phenomena such as shadow formation and making sound. To keep the attention of kindergarten (and younger and older) children, be sure to provide lots of open exploration time where they can be in contact with the materials to manipulate them and see what happens. Follow that open exploration time with a period of focusing on one question such as, do different materials make different sounds, how can we make a loud sound, or what makes sounds in nature (see the NGSS Appendix E and scroll down to PS4.A Wave properties) to see the summary of ideas appropriate for K-2; Sound can make matter vibrate, and vibrating matter can make sound. You will hold many conversations where you listen to children explain their thinking, and provide additional materials for investigation. Helping children document their ideas through drawings, video, and dictation, is another part of keeping children captivated!
See "The Early Years column, preK-grade 2" collection in the NSTA Learning Center for additional ideas from my columns, 124 collected thus far!
Best wishes, and thank you for doing science with young children,