From Child's Pose, lift the torso up and bring the legs between your hands, extending the legs in front of you.
Bend the knees, and lift your legs off the floor, bringing your knees in toward your chest with your shins parallel to the floor. Sit up as tall as you can, and slowly begin to straighten your legs. Your legs don't need to be straight since the action of keeping your spine long and drawing your belly in is what works your abs here.