How to do Bent leg kickbacks
Begin in a quadruped position on all fours with your hands directly under your shoulders and your knees directly under your hips. Look down at the ground so that your neck is in neutral. Engage your abdominals by pulling your belly button toward your spine to keep the spine in neutral.
Lift one knee up off the ground an inch and flex the foot. Then, press your heel straight up toward the ceiling while keeping the leg bent at 90-degrees. Raise that leg until the thigh is parallel to the ground. Be sure to engage your core to keep the hips levels instead of rotated.
Repeat for the desired repetitions, on both legs.