A lot of news I read about comes as no surprise to me, and sometimes sounds like a broken record, but a little reinforcement is never a bad thing.
Evidence suggests that a combination of dieting and exercise is a more effective way of losing weight after pregnancy than just dieting alone. Returning to body weight gradually after giving birth seems to be important, because women who regain their pre-pregnancy weight within six months have a lower risk of being overweight ten years later.
Also, exercise helps improve heart health, which is always a good thing since you're going to have a toddler to run around after in a few short years. If you're not comfortable leaving baby with a sitter while you exercise, grab the stroller and go.