If you're serious about fitness, consider joining a walking or running group in your area. You can find a listing of groups on www.seemommyrun.com. Moms walk/run at various paces and distances with and/or without their little ones.
Can't find a group in your area? You can start one for free. As a leader, you'll get free web space and downloadable promotional materials. Plus, you get to pick the time and days.