I ate what I wanted to and now Im paying the price !I have Diabetes,Colitis,weak knees, 14 kidney stones in both kidneys And sleep apnea.
I agree with Oak Dont let our kids get this way 
i'm 47. ate what i wanted, when i wanted to.
no diseases, no knee problems, no kidney problems, although i do have sciatica flare up every so often.......but that was originally from me falling off the back of a tow truck.
the biggest thing with kids and not letting them get fat is
1) get their butts OUTSIDE and ACTIVE
2)if they're aslready showing some weight problems, then get them eating leaner foods
3)try to teach them from your mistakes.
my brother is teaching his daughter this way. she's 9, and super/crazy active.....and is outside whenever she can be. when i visit, she wears me out. she's like an energizer bunny......but then my brother brought her up that way. he tries to keep her eating healthier than he did, but lets her have what she wants sometimes...even if it is considered "junk" food.