What works with Kids?

How to motivate them?  I know they're listening, watching, observing, even when they seem to be ignoring me or other adults.  I know this from my own experience.  I know this because they tell me later that they heard or saw me do something.

But why do some messages motivate while others shame?  Or create anger?

I worry about my oldest daughter, now 11. She's overweight and eats almost exclusively junk.  Her rail thin, eat like a bird, smoker, mother does not seem concerned.  My girl does not get enough exercise.  I think she knows she's overweight, I think she's concerned.  But she's not motivated.

I am scared.  I talk about healthy choices. I would like to get her out on a bike... anything...