I am currently a preservice teacher, and I am taking a science methods course. One of the chapters in our course textbook is dedicated to helping educators learn how to teach about magnetism using various fun and engaging activities. You may want to consider some of these activities to use with your second kindergarten class. The book is called Science Experiencers for the Early Childhood Years; An Integrated Affective Approach by Mary Rivkin and Jean Harlan.
One activity idea was to have students go outside with magnets and see what things in the environment are magnetic where one student tests the objects while the other student writes down what they discovered. Not only does this activity teach about the concept of magnets, but it also helps them foster their collaboration skills as they work in pairs. Another fun activity that was mentioned in my textbook was for teachers to provide students with different size magnets where they investigate which magnets are the strongest and which magnets are the weakest. One final activity that I thought was interesting was having students learn that magnets repel each other when one tries to place the same ends together. In this activity, students take two large magnets and try to put the same ends of the two magnets together (south with south poles) and then their opposite ends (south and north poles). This is very interesting and engaging for students because they get to physically feel the attraction and the resistance of the magnets.
Hopefully these are some exciting ideas that will keep your students interested in the topic and continue to motivate them to learn.