It is really hard sometimes and some weeks, I do none at all because we can't quite coordinate it.
DH comes home early one afternoon a week and I go to the gym while he gets the kids their dinner and baths them. I'm back for the evening feed. If he's later, I jump on my treadmill.
I also try to go to the gym at least once on the weekend and again, DH stays with the kids (usually during DS nap time).
I agree about the Nike training centre app tip-I was in soooo much pain after doing it so clearly it works!! You can do it in your lounge/backyard and I did it while DD (nearly 4) played in the backyard near me. Now to find some motivation to do it again...