My latest pregnancy left me with quite a few aches and pains and I had to start completely over with my excercise routines. Instead of running, I started lifting weights with the help of a coach at the YMCA and it has made a huge difference. For the first month I used no-impact machines for cardio workouts.
I'm now able to jog on occassion without feeling like my knees might collapse under me at any point. My back doesn't jiggle when I go over bumps anymore. I can wear a good deal of my old clothes. And I'm not nearly as tired as I was--although that might be becuase both of my children usually sleep through the night at this point.
I'm not ready to go to the beach and feel as carefree as I did at 20, but that may never be the case. And there are new wrinkles on places like my stomach that I notice now that some of the fat is gone. But still, I'd rather be wrinkly and fit than have taut skin simply becuase it's being stretched from the inside out.
Go for a walk. Without your children. It really does make you feel better.