It seems like a terrible battle sometimes, doesn't it. You can do it!

What has worked for me, so far, is to work with someone else who wants to lose weight. I've worked with my MIL before, and that was great - we both lost 30lb. (13-14kg, I think?) We would get on the scale once a week with the other person there, and whoever didn't lose weight had to make dinner for the other family. I've got another 20lb to lose, so right now, DH and I are having a contest - first one to take off 20lb wins. (We haven't set a prize - just bragging rights, I guess. ) That really helps to keep me motivated. As far as diet goes, I don't think you need to try a "special" diet - you need something that you can live with for the rest of your life. As so many have said, it's a lifestyle change. So look at what's unhealthy about your diet. Are you getting enough fresh fruits and veggies? Are you eating too much salt, sugar, fat, and processed food? Are you getting your protein from low-fat sources? (ie. lean meats, legumes, etc.) It's not always about eating less, it's about choosing the right things to eat. And that WILL make you a healthier person all around. Read the labels! Check the calorie and fat content.
Oh - and I've found that making sure I take in 8 cups of water really helps to keep me full, and take off weight. I HATE water. But I've got a pitcher on the counter which I make myself empty every day.
As far as exercise goes, I also find it really hard to get out with little ones. (I've got three at home) I've gotten a couple of exercise videos which I can do when the kids are playing. My favourite is an exercise ball one, because it's not too long (25min) and it doesn't require a lot of floor space. If you look around, I'm sure you could find something that would fit your needs. If you need a motivator to keep you doing it - ask a reliable friend or family member to call you and ask if you've done it, or do it with you three (or more) times a week.
About going for walks - yes walking at toddler speed hardly feels like a work-out, but just getting out and going somewhere will help somewhat. Do any of your kids ride bikes? That speeds things up a bit. I sometimes have my oldest DD ride her bike, while I pull the younger two in a wagon.

Those are my best thoughts for right now, and I'm sure some of the other lovely ladies will be able to give you more helpful suggestions.

All the best with losing that weight!