Also a mother with a young daughter. I am exercising on a recumbrant bike for 30 minutes a day, but I do like 7 minutes chunks, take a break, get some water and go back. Or if there's a tv show I really want to watch, I'll bike during the commercials. It's easy to add up to 30 minutes like this, and it doesn't have to be all at the same time.
From what my doctor has said, any exercise is better than none.