I am an RN that works night shift as well. The biggest difference between us is that I don't have kids. I have been working really hard to lose weight and eat healthy as well. I have limited eating out to once a week and drinking more water. You're going to have to cook before your shift and bring a lunch. If you work 2 in a row then you have to cook enough for 2 days. Or wake up early on day 2 to prepare food.
I've also been working out AT LEAST 3 days a week. I workout on my off days (you can while the kids are at school) and if it's not a back to back shift I'll workout in the morning before my shift. Sometimes if I'm feeling good on day 2 or 3 in a row, I'll wake up early (about 3) and throw on a workout DVD before work.
I also joined a 24 hour gym so on nights where I'm restless I can go to the gym at anytime.
It's really hard with our schedule but like with others, it's a mind thing. You have to really want it. I used the excuse of time before but when I started making time for it I realized that I couldn't use the excuses again. Because there is time.
It's hard but it's doable.