I am having similar issues. Something someone suggested here once was dancing to the Wiggles with your toddler, LOL! My DD loves it when I dance with her and I often end up holding her while we bop about. It's exhausting, so must be a great workout Only problem is that I want it to be over before she does, LOL!
Other thing I have tried is aerobics DVDs. Borrowed a couple from the library before Christmas and I would do a 20 min workout if Phoebe had gone back to bed after an early feed and Natty hadn't gotten up for the day yet.
But I still struggle too... I keep telling myself that as long as I don't put on more weight, I can sit tight and lose it later when the kids are a little bit older. But I am the procrastination queen
GL!