Lose weight and get a tummy tuck.  Half that flap is fat on the belly put there by the pregnancy.  You can have rock hard abs under a layer of fat and look pouchy.  The other half is loose skin.  All that skin that was on your ginormous belly at 40 weeks is still there just flopping around.  It does not go away unless cut away by a surgeon.  I had it done and the piece they removed was HUGE!  About 6 inches by 20 inches or so.  I am only 5 foot 2 inches tall, weigh 16 lbs and my waist is 27 inches.  So for women who get bigger or taller to being with the extra skin is gigantic.  Here is the best aprt, I got a hysterectomy when I had it done.  So it was free.