No matter how hard you are working doing exercise and crunches, the layer of fat masking a six pack won't come off unless you are eating right. Try to make sure you get in 4-6 smaller meals consisting of high, lean protein (chicken, fish, egg whites) and healthy carbs (like yams, brown rice, broccoli).
Make sure you do cardio (running, walking on a treadmill, or maybe even chasing the kids around the yard!) for 30-45 minutes a day, minimum three times a week. If you really want it to come off, try to do cardio 4-5 days a week. Don't give up, it will take awhile. But then again, it will all be worth it once you get that nice flat tummy you have been wishing for!