I try to excercise while my son is taking a nap. It's hard to get into a routine because his naps vary from day to day.
Sometimes there's just no time, but I take the stairs two at a time when I am going up and down doing laundry and I try to stretch and work out while doing housework. Eg. lunges while vacuuming, stretching while putting away dishes, walking around in high heels to tone my calves etc...