Hi,
I too have the same problem....Thanks to being overweight AND having had 4 kids!

I have had a lot of success toning with Pilates. It strengthens your core muscles (abs) and can be quite a work-out. I bought the Pilates for Dummies DVD on half.com and and ready to move into something more complex. I combine Pilates 3x a week with cardio 3-5 times and have really firmed-up.

Hope this helps!
Catherine