Hit the floor for basic exercises that work the core: Sit-ups, push-ups, and planks. Kids can do traditional abdominal crunches, bicycle crunches, legs-up sit-ups, and more. There are so many variations on the classic sit-up.
Kids can also learn to do basic push-ups and planks to strengthen their upper bodies and core muscles in the abs and back. Modify traditional push-ups by keeping knees on the ground, as needed.
As with other exercises like squats and lunges, incorporate these into games and other exercise activities (like circuits and races) to keep kids engaged and having fun.