As easy as this exercise may look, you would be surprised on how challenging it can be post pregnancy to lift your knee/or leg. You will find just how much weak your hip muscles are. The goal as you feel your muscles get stronger, is to be able to lift your knee higher without jeopardizing your form. Keeping your posture upright, and core tighten through the raise. Keep your foot flexed, not pointed.
2 sets of 5 reps on each leg. Once you feel more controlled with hip stability and balance, you can increase the reps.
**The only time a new exercise should be introduced/transitioned into is when the current exercise is mastered. You know when you have mastered that exercise when YOU can control that exercise and the intended muscle(s).