I've had 3 kids; I empathize with your wife on the belly thing. I don't think my stomach will ever be what it was pre-pregnancy.

OTOH, my trainer is 50, also the mother of 3 kids and has a washboard stomach. I will never look like her, but I've had tremendous success with following her plan of 200 ab crunches a day. Yes, I said a day. She's got a variety of various torture...um I mean...exercise techniques that work every muscle there from upper abs to lower abs to obliques. I started with 50 a day and worked my way up to 200.