I have 4 kids, all 15-21 months apart.
It really is tough to find time to work out, but now that they are getting older, it's getting easier.
My advice is to just do what you can, when you can. Perhaps you could get them to nap at the same time and steal 30 minutes to work out then?
Also, try to remember to get enough rest. I know that's easier said than done.