Childhood obesity success stories?

[AChickenCalledKorma]

DD2 has finally admitted to me that she would really like to learn to eat more healthily and tackle the excess weight she is carrying. This is something of a breakthrough. She definitely needs to get it under control.

I'd really love to hear anyone's success stories about how to help a child break out of unhealthy eating habits. I know there lots of advice online but I want to hear what WORKS!

She's 12 and has always put weight on very easily but it's climbed a lot in the last couple of years. We've been trying to help, without giving her a complex, but not getting very far. It doesn't help that her older sister and father are both very slim and can pack away junk without apparent consequences. Or that I am very overweight and have never managed to conquer it either. But we've agreed to make it a joint project!