This problem is common among post partum moms. It may not just be "abdominal fat." One of the most common reasons for this actually starts with the pregnancy - in 98% of women your rectus abdominus splits creating a separation called a diastisis.
It splits in three places along your abdomen - for most women its between 2 and 5 fingerwidths. It does not come back together on its own. With this separation - there is nothing that hold your "innards," like intestines stomach from protruding outward. That would be the purpose of the now-split abdominal muscles.
So while there generally is a little bit of fat - it is the separation of the abdominal muscles, the protrusion of everything inside that is causing this to happen. Also - incorrect "crunches" (terrible for post partum women) and some incorrect pilates can contribute to an even large diastisis - 6 or 7 fingerwidths, as well as "jack knifing" out of bed. The Tupler Technique is the best way to learn to fuse your stomach muscles back together and bring everything back IN with specific and intrinsic exercises designed for post partum (and pregnant) women. There is a great book called, "Lose your Mommy Tummy" by Julie Tupler that I highly recommend.
Or if you are close to my area - I teach the "Mommy Tummy" class in the H-F Park District. Our recent session just started last night at 7:30 - you can still get in.
I was able to bring my waist size from a 32 inch waist to a 25 inch waist doing the specific exercises consistently - it took about 4 months. Well worth it - and that was after baby #2.
Hope that helps - and good luck!!!