I think you teach by example.

You make low carb meals and have good low carb snacks available and let them learn how to be healthy by your example not instruction. Forcing never really works - how many of us were put on diets by others before we were ready to make our own decisions about this.

My history was that my youngest sister was hyperactive and my whole family was forced to change our eating to have no artificial colors, flavors or refined sugar in the house (by the way this really works much better then ritalin for moms out there feeding your kids those juice boxes). But for me... I dreamt of the things I would eat outside the house and became a closet eater - also I am still quite obsessive about foods since that time.

I'm only 5'4" and weighed over 260 by the age of 23.

Just another perspective.