Sleep! Yes, sleeping will keep you fit.
Try hard to get at least 6 consecutive hours of sleep...aim for 8! (I don't think I've slept for 6 hrs straight in 5 years!). This is, what I think, makes those last 5-10 baby pounds so hard to shed.
Basic tips: Do what you do for your kids.
Set a bedtime...and keep it as consistent as possible.
Set a bedtime routine...bath, read, yoga, mediation.
Make sure to relax during your day. And take a rest time during the day...even if that means 5 mins at your desk listening to quiet music, drawing a picture, or just closing your eyes.
While the kids are napping/resting...you too (Just say no to laundry!)
At the end of the day...take 5 mins to do a family stretch and yoga session (just some deep breathing and long stretches)
Make a point to sit down while you drink your morning coffee or afternoon tea.
Rest and relaxation are just as important as fat-burning cardio work.