Start with two sets of 10-12 repetitions, three to five times a week. Add extra reps or sets as you get stronger. To work the muscles along the sides of the abdomen, turn to the right or left as you curl up. If you are working the abdominals hard, you should strengthen your back, too, with back extensions or other exercises. And don't forget to stretch.
Flexibility is as important as strength.
I'm a mother of five and have been working out three times a week. I've toned up and lost weight but can't seem to get rid of my belly, stretched from pregnancy. You have a mother's body now, which is something to be proud of. But you probably see people on television and in magazines you want to look like. Understand that most of those people are dedicated athletes.